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.