Tuesday, April 30, 2013

Shot Differentials Of Non-Playoff Teams 1995-2013

One of the more disappointing aspects of the hockey stat revolution, if it can even be called that, is that time stops in October 2007.  Corsi data goes back no further.  Were we to make a graphical representation of our knowledge, we'd have a section labeled October 2007-April 2013 and outside of that would be tigers, griffins, wyverns, and other mythical creatures marking unknown territory.  It's a bit of a pin in the balloon of the certainty with which we stat types speak that we have to say things like 'Since 2007-2008...' - I mean, it's a year we all remember pretty well.  It's hard to be blown away by anything in that range.

I consider the modern era and thus the Corsi revolution to have begun in around 1995-96.  Standup goalies were on the way out, the neutral zone trap was in vogue, and we no longer see teams who win the Stanley Cup with a negative shot differential anymore (like the 80s Oilers).  Plus we got 4 more expansion teams which significantly altered one's chances of making the playoffs - before the second round of expansion, 61.5% of teams made the playoffs, now we're down to 53.3%.  I just wanted to see how important shots were in a grander scheme than the last six years, so I went all the way back to 1995 and with some hockey-reference finagling, looked at all the non-playoff teams and their shot differentials.

GIANT CAVEAT:  I realize that these are loaded up with score effects - teams with poor goaltending are more likely to have good shot differentials because they trail in games more frequently, and teams who miss the playoffs are also likely to be trailing more often.  Still, taking a wide view of this data, I think we can still learn a lot from it.

Of the 231 teams to miss the playoffs in the years between 1995 and 2013, 55 had 50% of the shots or better.  I didn't run a similar study on the playoff teams to see how many of them had positive shot differentials, but it's pretty clear it's a substantial number.  Of those teams who had 50% or better shot percentages and missed the playoffs, 27 of them had made the playoffs the year previous, with an average shot differential of 50.4%, and won an average of nearly 3 playoff games (this counts all teams, whether they made or missed the playoffs, so an average of 3 is pretty good).  The 1996 and 2013 Devils, 2003 and 2007 Carolina Hurricanes, 2004 Mighty Ducks of Anaheim, and the 1999 Washington Capitals are six teams who missed the playoffs after having reached the Cup Final the year before, all of whom had shot differentials over 50% the next season.  They are also 6 out of the 7 teams who've missed the playoffs after making the Cup Finals the year previous - the other one, the 2006 Oilers, had a positive shot differential the year before their Cup season.

Two teams continually missed the playoffs with a 50+% shot differential - the late 90s Calgary Flames and the late 00s Toronto Maple Leafs.  The obvious culprits are terrible goaltending and mediocre shooting - we all know the late 00s Leafs had wretched goaltending in the form of Andrew Raycroft and Vesa Toskala, and the Flames fared no better with a murderer's row of Trevor Kidd, Rick Tabaracci, and Fred Braithwaite.

So how did teams do the season after missing the playoffs with a 50+% shot differential?  Not as well as they had done the season before missing the playoffs.  Their shot differential is about the same, but only 21 of 52 teams made the playoffs, and all teams only averaged 2.13 playoff wins.  However, only 29 teams maintained the 50+% shot differential, and 18 of those made the playoffs.  This means that only 3 of the remaining 23 teams who shot worse than 50% made the playoffs the next season.  Since poor goaltending is a likely culprit in most of these teams missing the postseason to begin with, it's not that surprising that they couldn't be saved once they fell under the 50% threshold.

I wanted to look at teams with sub 50% shot differentials to see how they do the year after, but I think that is unfortunately mucked up by the fact that this era has a bunch of expansion teams who were pretty likely to struggle for several years.  I think we can get by with just Fenwick/Corsi numbers to examine that phenomenon.  Regardless, if you have a 50% shot differential or better, you're likely to make the playoffs, and if you didn't make the playoffs with that shot differential, you're likely to make it the next year if you can maintain that level.  There's anomalies for sure - the late 90s Flames, the late 00s Leafs, and the 03 and 04 Hurricanes who were particularly ghastly for a team that managed a positive shot differential - but shots are good.  Outshooting the other team is good.  You tend to make the playoffs if you do it and you tend to miss the playoffs if you don't.

Friday, April 19, 2013

A Note About Alex Ovechkin's "Resurgence"

Thus far, one of the most talked about stories of the shortened NHL season has been the resurgence of one Alex Ovechkin. Currently on pace to rival some of his gaudy goal totals from 2005-2010, the Great Eight has found twine 28 times in 44 games, good for a 52 goal pace in a normal 82 game season. During this, his age 27 season, Ovechkin is again producing like his 24 year old self.

Since we know that players generally peak around age 25, the inner skeptic fueled me to take a deeper look into just where Ovechkin's sudden spike in production is coming from. Following the lead of the fine folks at Russian Machine Never Breaks, below is a breakdown of Ovechkin's 5v5 and 5v4 numbers in 2013 compared with his 5-year averages from 2007-12 (numbers via stats.hockeyanalysis.com).

Ovechkin 5v5
2007-12 (Avg)25.825.6254.412.5610.1014

Ovechkin 5v4
2007-12 (Avg)13.815105.218.040.1312

There are two points to take home: first, Ovechkin's goals are coming less from even strength play, as his shot rates have slightly improved from last season but still fall below his insane 5-year average. While it's true that even a slightly mortal Alex Ovechkin still shoots with the league's best, Ovie's declining 5v5 totals just aren't in line with what we'd expect from 50-goal Alex Ovechkin.

Second, Ovechkin is shooting a hot 23% on the power play this season. Compare that with his 5-year average of 13.12%, a number closer in line with the league average 5v4 scoring rate, and we better understand why 50-goal Alex Ovechkin again walks the earth. Chris Gordon's observation that
The goals must come from somewhere else, and they do. The Caps feed him the puck so he can launch a quick shot from the circles, usually on the power play.
is spot-on, but comes with a "yeah, but..." attached if we're to look toward the future.

It's very possible that Alex Ovechkin is an above-average power play shooter, but approaching 10% better than league-average is far less likely. 50-goal Alex Ovechkin may have returned in 2013, but when it's entirely on the heels of something as volatile as PP SH%, next season's narratives almost write themselves. If Ovechkin can sustain the increase in PP shots he's getting in Oates's system, 40-goal Ovechkin may have a victory lap or two before Father Time reigns him in. However, projecting a player like Ovechkin to sustain this scoring rate becomes far less certain when he's depending on more goals to come from the inherent volatility involved with scoring on the PP.

Thursday, April 4, 2013

Special Teams Shot Differential

Mike 'Doc' Emrick purports to hate numbers and mentions how bad he is with them, but one of the numbers he liked and mentioned often during his regular broadcasting days was something called Special Teams Index - it was quite basic, you summed a team's power play percentage and a penalty kill percentage, and voila - there was your Special Teams Index. 100 is average, anything 5-10+ points above is real good, anything 5-10+ points below is real bad. Easy stuff, right?

These days, we know a bit better - we know that penalty killing and power play success is driven by the number of shots a team is able to both get and prevent and that teams don't have a huge amount of control over either shooting percentage or goaltending. Furthermore, power play and penalty killing percentage don't take into account how many short handed goals a team either allows or scores, much less shots. So knowing that shots tend to be more meaningful than goals when we think about what's going to happen in the future, I whipped all these new items into something I call Special Teams Shot Differential - It's the sum of a team's power play shot differential (Shots For per 60 minutes - Shots Allowed per 60 minutes) and penalty killing shot differential. Here's a table of the whole league, with their 5v4 and 4v5 goal differentials on beside it (numbers courtesy of behindthenet.ca, which is updating wonkily and thus these numbers may be slightly incorrect).

TeamShot DifferentialGoal Differential
CGY -3.94

Now I haven't included power play differential in this at all, so some things will be skewed - some teams who are close to 0 in shot differential may be generating more shots than they allow by virtue of drawing more penalties and vice versa. Still, we see the teams who have a bad shot differential tend to give up goals on special teams, and teams who have good shot differentials score them. Most surprising on this list to me was Anaheim, who've led a charmed existence at even strength but are really quite good on special teams and are not fully seeing the benefits of that (Their -26 PP/PK differential is the culprit here - ditto Boston, who's having a remarkable year on the PK). Still, though, we see just how little 5v4 and 4v5 power plays and penalty kills matter in the big picture - few teams have a differential plus or minus 10, those that do are largely driven by luck, and we're nearly halfway done with a regular season.