Power Play Trends: Why We Shouldn't Focus on Merely Results

As I was watching the CSN-Philadelphia broadcast of the Coyotes/Flyers game on November 18, during a break in the action of the Flyers’ first Power Play the following chart was shown to the viewer, entitled “Special Teams Reversal.”

	First 8 Games	Last 9 Games
Power Play	27.5%	9.3%
Penalty Kill	82.9%	90.2%

Presumably to reinforce play-by-play voice Jim Jackson’s comment at the beginning of the Flyers’ first man-advantage that the power play had been “struggling here of late,” I see a completely different trend when I look at the same numbers.

As Gabe Desjardins pointed out in this article, “The PP is all about directing shots on goal,” and I’m feeling daring enough to assert that the PK is all about preventing shots towards your own net. Looking at the Flyers’ shot rates per 60 minutes on special teams during the first 17 games once again thanks to JaredL, it becomes less surprising why such a reversal took place:

	First 8 Games	Last 9 Games
PP SF/60	50.7	40.7
PK SA/60	39.4	39.6

As of today, if the Flyers were to sport 50.7 SF/60 on the PP, they would rank 12th in the NHL according to BTN and 40.7 would put them 28th. Their PK numbers would rank them 2nd in both occurrences. What is more, if we look at the shooting data from the same span we see another trend bolder than Jaromir Jagr’s Movember ‘stache:

Power Play

	Shots	Goals	Shooting %
First 8 Games	53	11	20.8
Last 9 Games	46	4	8.7
Total	99	15	15.2

Penalty Kill

	Shots	Goals	Save %
First 8 Games	43	7	.837
Last 9 Games	44	5	.886
Total	87	12	.862

In addition to their more potent shot-generating PP in the first 8 games, the Flyers were shooting at an unsustainably high rate and opposing goalies were stopping an unsustainably low number of shots. The numbers are more reasonable on the PK, though the Flyers’ opponents were still running a bit warm with their shooting. As the sample size began to grow, we see the Flyers’ shooting percentage come back down to Earth as their opponents began to stop a more reasonable number of shots. Philadelphia’s PK numbers also even out by a bit less of a margin as we might expect based on the unit’s consistency.

Though such a turnaround may be alarming to those who still choose to judge power play success based on results, the fact of the matter is that the Flyers PP of the first 8 games was merely a mirage. As the season rumbles along, expect the Flyers’ special teams to mirror the second half of CSN’s chart rather than the first.

Weekly Power Rankings #1

Every Sunday night, I will be posting updated objective power rankings. Instead of only focusing on 5-on-5 play with the score tied, for each of Corsi and Fenwick I use a logit model to take into account score effects, schedule and special teams. Using the numbers the model spits out, I generate what each team's expected even-strength score-tied Corsi and Fenwick percentages would be if they played a balanced schedule. It is important to note that my model ignores goaltending. Also, while it adjusts for special teams, it does not reward or punish teams for getting there. So teams that are mediocre on the power play but get there a lot or bad on the penalty kill but very disciplined will be underrated.

As usual with these sorts of things, they should get better as the season goes on and we get more data.

A handful of teams jumped out, that I'd like to comment on:

- Colorado has put up decent, much-improved possession numbers at even strength. In special teams they have been above average getting pucks toward goal on the PP and very strong suppressing shots on the PK. They have not gotten the goaltending or bounces at either end. I think this ranking overrates them, but a deeper look points to them being better than I initially thought. Perhaps mediocre is more accurate than bad.

- The Jets are another team that this ranking puts substantially above where they are in the standings. They have put up better than average possession numbers but whatever combination you like of bad bounces in their own zone and bad goaltending has done them in. They have also haven't been disciplined, ranking dead last in the league at times shorthanded. If the team hadn't moved, this would be familiar to Jets fans since they had a similar pattern in the second half of last season.

- They won't win the rest, but I think we can expect the Canucks to continue their rise and pull themselves up near the top of the standings.

- The Rangers are in trouble. They've had an unsustainably high save percentage and a ridiculous shooting percentage at even strength (9.9%), both of which are almost certain to drop. They are getting dominated 5-on-5 and are fourth worst in the league in shooting rate 5-on-4 (BTN). I don't see them making the playoffs.

Here is the ranking, sorted by Corsi%

Rank	Team	Corsi%	Fenwick	Fen Rank
1	Detroit Red Wings	57.9	57.6	1
2	Vancouver Canucks	56	55.1	3
3	Pittsburgh Penguins	55.3	54.8	4
4	St. Louis Blues	55.1	56.5	2
5	Boston Bruins	54.1	53.1	6
6	Chicago Blackhawks	53	54.4	5
7	Colorado Avalanche	52.8	52.4	8
8	San Jose Sharks	51.8	52.7	7
9	Washington Capitals	51.6	50.7	12
10	Philadelphia Flyers	51.4	51.6	10
11	Winnipeg Jets	51	51.8	9
12	Florida Panthers	50.8	50.2	13
13	Montreal Canadiens	50.7	51.5	11
14	Ottawa Senators	50.1	49.9	14
15	Phoenix Coyotes	49.7	48.9	18
16	Los Angeles Kings	49.7	48.4	19
17	Columbus Blue Jackets	49.5	49.6	16
18	New Jersey Devils	49.5	49.9	14
19	Buffalo Sabres	49.2	47.6	24
20	Calgary Flames	49.2	49.3	17
21	Toronto Maple Leafs	48.1	47.8	22
22	Carolina Hurricanes	47.9	47.7	23
23	Edmonton Oilers	47.4	48.1	21
24	Dallas Stars	47	48.4	19
25	Tampa Bay Lightning	46.3	46.5	25
26	New York Islanders	45.6	45.3	28
27	Minnesota Wild	45.1	46	26
28	New York Rangers	45.1	45.8	27
29	Nashville Predators	44.6	44.5	29
30	Anaheim Ducks	44.5	43.9	30

Anomalies: Why Are Crosby's Possession Numbers Merely Good

This will perhaps be the start of a continuing series in which we analyze and discuss strange things we've noticed about hockey statistics. A feature of these articles is that we won't have all the answers, so comments and discussion are strongly encouraged.

In this installment, I want to discuss something that has irked me since I first got into hockey analytics. After reading about Corsi and Fenwick stats I went to BTN to look at the numbers for my favorite team, the Pittsburgh Penguins. I was quite surprised by how bad the team was according to these metrics, this was in the Therrien days, and in particular Crosby's numbers were downright mediocre. They have improved since but over the last two seasons, in which he played a season and a half, his even-strength Corsi/Fenwick stats are merely good instead of great. To state the obvious, he is considered by many to be the best player in the game and nobody reasonable would put him outside the top 5-10 players, head injury aside. What gives?

5-on-5 Corsi

Here are his Corsi numbers from 2007-2008 through 2010-2011. I include his rank among forwards that played 40 games or more for the given year.

Season	Corsi On/60	Rank
2010-2011	8.55	64
2009-2010	12.55	29
2008-2009	-0.21	186
2007-2008	2.35	140

Even with the improvement, including the huge points streak taking up much of the 2010-2011 season, you can see that his stats aren't close to the elite level most everyone would put him at, including us nerds. I have a couple possible explanations, but would love to hear from you if you've got more.

Weak Linemates

For Pens fans, a frustrating part of having so much strength at center is that there is not a lot of money to go around for wingers. If you look at the guys consistently at the top of the Corsi rankings, you tend to see pairs or groups of top guys that play together or perhaps an elite player with at least one good player. Examples include a number of Detroit combinations, whichever combination of Kane, Toews, Sharp and Hossa you like, the Sedins, Ovechkin with Bäckström and Kesler with Raymond. Crosby has spent most all of his time with guys like Dupuis and Kunitz who aren't bad but are definitely role players and don't compare well to those names.

Let's take a look at the Corsi QoT for selected players in the last 3 full seasons. Corsi QoT is the average Corsi rating off all skater teammates for the player's ice time. It isn't perfect because a player influences his teammates' ratings but gives a rough idea how good the teammates are.

Player	2008-2009	2009-2010	2010-2011
Sidney Crosby	-3.628	5.297	5.779
Alexander Ovechkin	12.953	8.438	4.013
Pavel Datsyuk	17.246	12.229	7.363
Jonathan Toews	11.629	14.858	8.437
Henrik Sedin	1.368	7.435	8.28
Ryan Kesler	-0.149	7.021	7.624

You can see that going by this metric Crosby's teammates have not been as strong as those of other elite players.

An exception to this rule is that he has played a bit of time with Malkin. How has that duo been? I haven't pulled data from 2007-2008, but I do have it from the last three years. Here is a chart with their Corsi rates together. Unsurprisingly, they are all much better than Crosby's overall numbers.

Year	Corsi%	Corsi/60	Minutes
2008-2009	47.5%	-5.647	393
2009-2010	56.2%	16.377	202
2010-2011	62.0%	32.047	163
Total	53.4%	8.317	758

I'll have more on that 2008-2009 season in a bit, but in the last two years for the time they've been on the ice together they have dominated. I didn't list the score-tied numbers but they are actually pretty similar.

Coaching

People are making similar arguments for Ovechkin this year, which I think is at least in part an overreaction to some brutal shooting luck, but it seems like in the early years the cautious, defensive approach espoused by Michel Therrien may have held the Penguins back. It's beyond my area of expertise to analyze the particulars of this, but there are data to back this up.

Courtesy of time on ice here are the Corsi percentages (Corsi shots for divided by Corsi shots for and against) the seasons before during and after Bylsma took over for Therrien. While the Pens were and still are a young team, the jump is pretty big and the 2008-2009 season is damning.

Season	Coach	Corsi%
2007-2008	Therrien	45.6%
2008-2009	Therrien	46.0%
2008-2009	Bylsma	52.8%
2009-2010	Bylsma	52.2%

A problem with this analysis for the 2008-2009 season is that Gonchar, Pittsburgh's best defenseman that year, was out most of the early part of the season coming back right around the time Bylsma took over 25 games from the end. Here are the numbers from 2008-2009 for all time in which Gonchar was off the ice, whether or not he was in the lineup, under Bylsma and Therrien.

Coach	Corsi%
Therrien	46.0%
Bylsma	52.8%

For that 2008-2009 season, here are Crosby's on-ice Corsi numbers with each coach:

Coach	Corsi%	Corsi/60
Therrien	48.8%	-2.836
Bylsma	50.5%	1.205

Of course there are many many other factors like overall team skill going up and variance may have played a role. That said, based on these splits I think some of the blame for the first couple years goes to Therrien, or you might say the praise for the last few goes to Bylsma.

Putting It Together

Let's look at Crosby's Corsi numbers with and without Malkin since Bylsma took over:

Situation	Corsi%	Corsi/60
With Malkin	57.7%	20.239
Without Malkin	53.0%	7.12

That's in 421 minutes of ice time with Malkin, or over 7 full games worth of time. If Crosby played 75% of his time with Malkin then his Corsi% would be about 56.5% and his rate about 17. Both of these numbers would be right up at the top of the Corsi rankings.

Conclusion

These are my ideas, I'd love to hear more if you've got them. I'd also be interested in your thoughts on what I'm putting out there. I think the biggest factor by far is the relative weakness of the wingers. This is supported by how dominant Crosby was when Evgeni Malkin played the top-winger role for him over the last couple seasons.

Can Rinne Earn All That Money?

The Pekka Rinne contract extension a couple weeks back remains the most interesting off-ice move of the season. It touches on a lot of things we have written about and discussed behind the scenes, most notably the role of luck and skill in results and whether it's better to build a team by spending big on goaltending or leave that money for the skaters - see Matt's thought-provoking post on the subject. The Predators are also in a peculiar spot as a team that has spent near the floor in the past but now will perhaps change gears and spend closer to the cap. This is all happening, and almost certainly related to, with Weber (RFA) and Suter (UFA) coming up as free agents this next offseason. Chase covered the cap/budget impact quite well last week. There is a lot to unpack here and we'll be revisiting this deal, looking at Nashville's situation and trying to answer more general questions like how much top goaltenders should be paid over the course of the season.

In this article, I will look at how his contract compares to those of other top goaltenders, at least those paid like one. The question at hand is how much he has to contribute for his $7M a year to be reasonable compared to other big-money goaltender deals. I am ignoring several key things like regression to the mean that might impact the overall value of goalies. In other words, I'm not looking at more general things like whether goaltenders as a whole are overpaid, or even if Rinne will be but rather what he has to do for us to say he's not overpaid relative to other top-dollar goaltenders.

Everywhere Is WAR

The nice thing about analyzing goalies is that we have a large number of discrete events and while there are teammate, opponent and rink/scorekeeper effects, the strength of a goaltender's performance pretty much boils down to how well they stopped the puck in different situations. Goaltender analysis is more similar to hitters in baseball than it is to skaters in hockey. The metric I'll use is WAR, Wins Above Replacement, which is very similar to the baseball stat of the same name. The idea is to look at how many goals the goalie in question gave up and compare that to what a typical replacement-level goalie (think free agent paid the minimum salary) would have allowed on the same number and type (ES, PK, PP) of shots. We can translate this number into wins to see how many wins each goaltender gave their team over what a replacement-level goalie would have.

I'm far from the first to use this method. As far as I understand it, GVT follows a similar approach for goalies. For a few other examples, Gabe Desjardins did something very similar two years ago over at Puck Prospectus and there was a fanpost on the subject by DoctorMyBrainHurts at Gabe's usual home, Arctic Ice Hockey. Philadelphia's goalie issues and the signing of Bryzgalov motivated some similar work by our friends Kent Wilson and Geoff Detweiler. With skaters it's rather more complicated, but for goalie analysis this approach is pretty clearly the way to go.

This is already one of the longest intros of all time so I won't go too far into detail about exactly how I calculated this. For replacement level, I took took the combined results of goalies that were not in the top 60 in games started for each season after the lockout. Another difference between my work and the others linked above is that I use 5.52 goals per win instead of the usual 6.0, which I feel is more accurate based on regressing league points on non-empty-net goal differential since the lockout. This warrants an article of its own, which I'll post later this week.

What does $4+ million buy these days?

Capgeek only goes back a couple years and nhlnumbers, which I used, only stretches back to 2007-2008. In those four seasons, we have a sample of 60 in which a goaltender had an annualized cap hit of $4M or greater. Here is a scatter plot showing the relationship between goaltender wins-above-replcement and the cap hit minus the minimum player salary. Something to note is that there isn't a very strong relationship between a goaltender's cap hit and how much value in wins he turned out to provide to his team. This is a sign that maybe high-price goaltenders as a group are overpaid, but I'll leave that for future work as it's outside the scope of this article.


The regression equation you see tells us what we should expect a goaltender to produce for a given cap hit over the minimum salary. The last two seasons the minimum has been half a million dollars. Going by that, here is what we should expect out of goaltenders in this range:

Cap Hit ($M)	WAR
4	3.42
4.5	4.28
5	5.14
5.5	6
6	6.86
6.5	7.71
7	8.57

So 4 million dollars buys you about three and a half wins.

How productive must Rinne be?

And finally we are ready to answer the question at hand. How well does Rinne need to play for his contract to compare well to other high-dollar goalie contracts? Looking at the last row of the table, we see that producing a WAR of about 8.57 a year is about right. Here are his last 3 seasons, which comprise 167 of his 168 career starts:

Season	Starts	WAR
2009	49	4.75
2010	54	3.76
2011	64	11.17

This averages out to a WAR of 6.56 per season, far below the expected 8.57. However, there might be two reasons to be optimistic. His number of starts per year has gone up each season and even on a per-start basis his WAR was substantially higher last year than the first two. While our gut instinct may chalk the latter up to random variance, the starts going up each year is obviously important since it's hard to provide value from the bench or IR. This raises two issues, how much he needs to play to get his WAR up to the 8.57 range and/or how much his save percentage might need to improve to do so. Let's consider those separately.

Rinne has faced an average of 24.35 shots at even strength, 4.32 shots on the PK and 0.67 shots with the Preds up a man per start in his career up to the current season. Based on his career save percentages in these spots (0.928/0.877/0.903) and the replacement group's (0.907/0.845/0.908) he has a WAR of 0.118 per start. To get to 8.57 for the season, he would have to start about 72 games a year! Keep in mind that this would be starting almost every game without seeing any dropoff in save percentage from his career average. Only Lundqvist has gotten close to that many starts and based on what Rinne has done the last three years I think we can all agree that this isn't realistic.

So, then, it would appear that he has to improve on his already high save percentage that most of us would guess is over expectation. How much improvement? Let's take his 64 starts last year as the jumping-off point. If he faces the same number and type of shots per start as he has in his career thus far that would be about 1,877 shots a season. A replacement-level goaltender would allow almost exactly 3 goals per start, or 192 goals for the season. At 5.52 goals per win, Rinne would need to concede about 47 fewer goals to be worth 8.57 wins above replacement. This translates to a save percentage of 0.923. Here is a table with all goaltenders with a career save percentage of 0.923 or above, minimum of 500 games played:

Player	Starts	Career Save %

Just off the list is Dominik Hasek with a career save percentage of 0.922.

For his contract to be about about equal in value to other goaltenders making $4M a year or above, all Rinne has to do is play at the Hasek level for 65+ games a year for 7 years.

A Look at the Pekka Rinne Extension

This past Thursday, the Nashville Predators announced they had signed franchise goaltender Pekka Rinne to a 7-year, $49 million extension – the largest deal awarded in team history. After this season, Rinne’s average annual salary of $7 million will represent the highest cap hit for a goalie in the NHL, up from his $3.4 million number this season. On the surface, locking up a player that the franchise sees as “the best goaltender in the NHL” for the foreseeable future may seem wise, but there are a few underlying reasons that make this deal foolish for the Preds.

Let’s think about this again: 7 years, $49 million. For a team that is only spending $49,588,730 towards the cap this season and spent $50,903,696 last season, Rinne’s new $7 million cap figure would represent roughly 1/7 of Nashville’s entire budget. What is more, this doesn’t take into account the inevitable contract situations of both Shea Weber and Ryan Suter.

Weber, of course, was awarded a $7.5 million salary in arbitration this past summer and is entering his final season of restricted free agency. He will once again be arbitration-eligible and shouldn’t command a salary less than $7 million. Without signing him to a long-term deal making his cap hit more favorable, Nashville would likely be committing $14+ million to two players next season. Even if they choose to extend Weber long-term, I don’t see him taking much less than his current salary, further guaranteeing an emerging cap constraint.

Suter’s situation is equally sticky. He is set to become an unrestricted free agent next summer, the clear prize of the defensive UFA class. Considering there hasn’t been a defenseman of Suter’s caliber on the open market in quite awhile, he could easily command a salary upwards of $6 million for multiple seasons. Once again, if the Predators plan to keep Suter they will have to back themselves into a corner salary-wise.

Even worse, all of this hasn’t taken into account Nashville’s dire need for forward depth. If the Predators continue their trend of spending ~$50M relative to the cap, any combination of Rinne-Weber/Suter will easily cost $12-14 million and approach $20 million should they decide to keep all three. Here’s where it gets dicey – the Predators are already on the hook for 11 contracts next season (including Rinne) for a total of $30,710,833. Should they keep one of Weber/Suter, they will be at roughly $36-38 million with 12 players signed. Should they keep them both, they will be approaching $43-45 million with 13 on the roster.

This is where the rubber meets the road. If they choose to spend to the upper limit, the Predators would have roughly $2.8 million per opening to fill out a 20-man roster. If that number seems high, it probably is. It’s very rare for teams to field only 20 players on an active roster for lack-of-depth reasons. No team will go through an entire season with the same 20 players intact, and for each additional skater they chose to ice the Predators would lose about $358,735 per available roster spot. Also, for every $1 million below $64.3 million ownership chooses to spend, that $2.8 million number would drop another $142,857. I’m skeptical that the Predators are ready to step into the arena with the NHL’s heavy spenders just yet, meaning they could easily be looking at $1.6 million (or less) per salary opening just to ice a 21-man roster.

Previewing next year’s offseason, Nashville currently has 8 players not named Shea Weber set to become restricted free agents at the end of this season – seven skaters (4 forwards, 3 defenseman) and G Anders Lindback. Their current salaries total $9,004,167 which wouldn’t take into account any potential raises each player would earn. It is very unlikely Nashville will find the cap space to even address their RFA needs, let alone address their weakness up front in the UFA market. For a team that claims to be solidifying its future, the idea begins to look counterintuitive.

What, then, is the answer to the equation if both Weber and Suter can't fit under Nashville's cap? The difference between Weber's upcoming RFA status and Suter's UFA status may be the deciding factor here. If another GM wants to shoot Nashville an offer sheet for Weber this offseason, they would stand to lose at least two first round draft picks because of the high salary Weber would command. As we saw this past summer, GMs are very reluctant to offer sheet high-priced RFAs for this exact reason, thus giving Weber more certainty to be back next year. Should the Predators find themselves out of contention by the trading deadline, shopping Ryan Suter could fetch a ton of offers for a playoff run because of his affordable $3.5 million cap hit. While a trade may be the best option moving forward, if Nashville is in the playoff picture it seems less likely any deal would happen. Should Suter decide to test the UFA waters come July, the Preds may lose out on receiving compensation for his departure. If it became clear that he wasn't going to re-sign, they could trade his negotiating rights before July 1 but any return would be less than what they could get at the deadline.

Regardless of what happens to both defenseman this summer, there is no way around the fact that having Weber and Suter on the ice is a heavy positive for the Predators. While Nashville ownership claims to be making every effort to re-sign them both, having the Rinne contract on the books will make it extremely difficult. At the end of the day, $7 million is an astronomical salary for a goaltender, especially for a team on an internal budget. Without taking nearly all of that salary and pouring it into better options up front, it may be awhile before we see Nashville capable of producing a positive shot differential per 60 minutes at even strength. In the end, it was GOB who said it best:


Next up will be JaredL delivering your statistics fix by taking taking a deeper look into the actual values of Rinne and other goaltenders to their teams.

October Trends, A Week Late and Possibly A Dollar Short

I don't know if there was an equivalent in hockey for all you Canadian readers, but as a child I loved summer Sundays. That was the day the newspaper printed the statistics of all the baseball teams. Some guy I never heard of was hitting .353 - fascinating! Why's so and so hitting so poorly? It's easy to forget what it was like without having access to all the information you want, all the time. We're so awash in data that talking heads are constantly spinning narratives about what a particular hot or cold streak means. Well, I'm here to tell you what they actually mean.

I was doing some clicking around for this year so far, now that we're more than an eighth of the way through the NHL season - narratives are already emerging. I intend to make this a monthly column, and next time I won't think of the idea on the 4th of the month.

The Red Wings Stink Right Now

Will This Continue? No

Why: The beginning of the season is when people notice things. A team on a 105 point pace having a mediocre 10 game stretch in February gets noticed, but it's not alarming. That team is still a big favorite to make the playoffs. Anyway, the Wings' problem is simple - they're getting the shots but they're not going in. It's almost impossible to win consistently in this league shooting 5% at even strength, as the Wings are so far this year. During the Wings' losing streak, they're shooting 1.9% at evens - it's almost impossible to win this way.

Since I wrote the above, the Wings spanked the Anaheim Ducks, both on the scoreboard and territorially. They're going to be just fine.

Michael Grabner Is Perhaps Not The Tactical Genius I Thought He Was

Will This Continue? Yes

Why: Fortune favors the bold; predictors of others' fortunes doubly so. That's an Edward De Vere original quote that I just made up. Whatever the case, Michael Grabner's having a rough start to the season. 11 games, 3 goals, 0 assists, -4. What's most alarming are Grabner's 17 shots on goal through his first 11 games. I think Grabner will continue to be a play driver and dangerous forward, but I am not convinced that he is an elite player. I would not be shocked to see him end this year with 35 points over a full season.

Manny Malhotra Is Looking Like The Player The Rangers Threw Away for Martin Rucinsky

Will This Continue? Kind Of

Why: Manny Malhotra currently has 0 goals and is a -10 on the season. Last year, many close observers of hockey felt he should win the Selke Trophy. Malhotra starts his shifts in the defensive zone more often than just about any player in hockey - right now he has a Zone Start of 24.8%. Last year somehow he was a plus player in spite of this usage, but that was in part because of a .944 SV% while on the ice at even strength. I don't expect that to continue - while Malhotra will likely finish the year at or around -10 (right now his SV% ON is .844), it's really difficult to maintain a positive plus-minus when you're behind the eight ball that often.

Trends To Watch Out For:

Anaheim and Nashville do not look like playoff teams so far this year

While the Leafs are riding a ridiculous hot streak, they are also better than last season

Evander Kane just might be ready to break out

Triumph might write his post about playoff teams' records against non-playoff teams

Splitting Up Duncan Keith and Brent Seabrook

Outside of Patrick Kane's impressive move to the middle, perhaps the biggest story in Chicago's impressive 7-2-2 start has been Joel Quenneville's decision to split up Duncan Keith and Brent Seabrook. The natural reaction to a coaching move so major is curiosity - why would the Blackhawks decide to split up one of the game's best pairs?

Depth

The most obvious explanation is that the move is Joel Quenneville's way of mitigating the loss of Brian Campbell. On a simple level, separating Keith and Seabrook ensures the Blackhawks will play the vast majority of their even strength minutes with at least one of their superstars on the ice, especially given Nick Leddy's relative inexperience in playing top-4 minutes.

Development

It's pretty obvious that the organization is high on Leddy (Scotty Bowman compared Leddy to Phil Housley), and I can't help but think that their confidence in his ability to eventually play top-4 minutes helped to ease the blow of trading Brian Campbell, as evidenced by the team choosing not to sign or trade for any top-4 defensemen (I believe Montador was primarily signed to solidify the bottom pair, though he obviously has shown the ability to do well in a heavier role).

I think the surprise comes not from Leddy's presence in the top-4, but mostly from who is primary defense partner has been.

Strategy/Usage

I'll note from the outset that using QualComp or any variant thereof is useless at this point in the season. There is just too much variance in strength of schedule to draw inferences from those numbers. What I will use instead is PBP data (h/t Jared).

The first section of data only focuses on Zone Starts and their Corsi numbers based off of where they started a shift.

Keith-Leddy	% of TOI	Corsi Rate
Ozone Faceoff	13.6%	33.277
All neutral	79%	3.127
Dzone Faceoff	7.4%	-38.889

Seabs-Hjalm	% of TOI	Corsi Rate
Ozone Faceoff	13.3%	47.872
All neutral	74.6%	12.54
Dzone Faceoff	12.1%	-28.18

From here we can see that the Seabrook/Hjalmarsson line is much more likely to take a defensive zone draw. We can also see that the Seabrook/Hjalmarsson pairing has performed much better territorially, no matter the situation.

As I said above, I am not using QualComp or any variant of QualComp to adjust for the toughness of the minutes. Instead, I'll use forward pairing as a proxy, as the roles in which Chicago forwards are used are pretty rigid. As we can see below, the Keith/Leddy pairing is most often used alongside Jonathan Toews and Patrick Sharp in any situation. As for Seabrook/Hjalmarsson, the forward they play with most often is David Bolland.

Ozone	Keith-Leddy	Seabs-Hjalm
Toews	41.8%	30.6%
Kane	37.9%	21.9%
Sharp	44.8%	22.5%
Hossa	31.8%	12.8%
Bolland	12.6%	39.4%
None of above	5.5%	14.1%

Neutral	Keith-Leddy	Seabs-Hjalm
Toews	32.7%	19.6%
Kane	38.2%	26%
Sharp	33%	15.3%
Hossa	33.6%	23.1%
Bolland	14.1%	44.6%
None of above	16.4%	8.8%

Dzone	Keith-Leddy	Seabs-Hjalm
Toews	33.3%	10.3%
Kane	32.3%	21.2%
Sharp	47.1%	4.6%
Hossa	23.6%	21.1%
Bolland	21.9%	62.7%
None of above	9.1%	6.8%

As I briefly mentioned above, I believe we can validly infer that the Seabrook/Hjalmarsson pairing has played tougher minutes, mainly because of how much more likely they were to play with David Bolland, whose role for the Blackhawks is well-defined as a shutdown Center. If you guys feel this is an unreasonable assumption, let me know.

Results

Here are the results of the three centers, along with the rest of the ice time, with the Keith/Leddy and Seabrook/Hjalmarsson pairings. As you can see, the Seabrook/Hjalmarsson pairing has gotten better Corsi results with each of the top three lines in the small sample we have.

Forward	Pairing	Corsi/60	Time
Toews	KL	6.063	49.5
Toews	SH	21.352	28.1
Kane	KL	7.643	55
Kane	SH	22.222	35.1
Bolland	KL	2.841	21.1
Bolland	SH	10.154	65
None	KL	-2.857	21
None	SH	-4.604	13

Conclusions/Recommendations

To be honest there are numerous explanations for why the Keith/Leddy pairing hasn't performed as well as the Seabrook/Hjalmarsson pairing. The first is that Seabrook/Hjalmarsson have played together more (in previous seasons) than Keith/Leddy have and the disparity is largely driven by a lack of familiarity. The second is that Nick Leddy isn't as good (yet) as Keith, Seabrook, or Hjalmarsson - it is possible that Leddy is dragging Keith down a bit. Finally, this could merely be variance.

As for my recommendation, I honestly see no issue with keeping these pairings together. As I noted above, all 4 players are off to solid starts, and while there is no doubting the chemistry and effectiveness in a pairing of Duncan Keith and Brent Seabrook, the fact that the Keith/Leddy pairing has done as well as it has speaks volumes to both of those players. The eye test leads me to believe reason #1 above is the best explanation for why there has been a disparity in their possession totals. I believe that as the Keith/Leddy pair grows and each player becomes more comfortable with each other, the net result for the Hawks will be positive, couple that with the long-term developmental benefit of pairing Keith and Leddy, and I see no issue with continuing this pair.