“It’s funny because our game looks at numbers just like other games [...] but as much value as we assign to puck possession and how essential it is to winning, we really don’t have a numerical value for it that everyone can agree on. Remember when [A's general manager] Billy Beane started emphasizing on-base percentage in baseball? It wasn’t just a curious number; it changed the game. It redefined the type of player you wanted on your team. It’s coming in hockey; we just have to figure out how.”

That’s Ken Holland from Brian Cazeneuve’s SI column on the importance of puck possession. I don’t know if the Red Wings GM is being purposely obtuse with Cazeneuve or if he really isn’t aware, but the numerically inclined amateurs who cover hockey have been employing a quantified version of possession for years. It’s called Corsi.

I frequently discuss Corsi in my own articles here at theScore and elsewhere, but he’s a brief overview of the metric:

Developed by Buffalo coach Jim Corsi, it was originally designed to track goaltender performance. Corsi is a differential or ratio of all shots at the net (shots, missed shots and blocked shots) for and against while a player is on the ice (usually at even strength). It is a proxy measure for zone time: high Corsi players spend more time in the offensive zone and vice versa.

Gabriel Desjardins does a more thorough overview of Corsi here. I also have a look at the Calgary Flames individual possession rates and scoring chance numbers from this past season in this post. Of note: the correlation between Corsi and scoring chance ratios was just south of 0.7 in the 79 games I counted this year (a number which is both strong and statistically significant). Others have found even higher correlations between Corsi and chances in the past. Objective NHL’s JLikens determined the strength between outscoring and outshooting over large samples in this investigation. These links are merely scratching the surface on the body of work that has been done to establish Corsi’s value as a metric.

Cazeneuve’s piece highlights many of the reasons possession has become more important in a post-lock-out NHL: the crack-down on obstruction, the rush to imitate the success of the Detroit Red Wings, etc. He interviews more than a few notable NHL GM’s including Holland, Mike Gillis and Steve Yzerman, none of whom apparently agree on a method to reliably track puck possession, even though they universally agree it’s a key to winning.

This means one of two things: either the league’s executives are actually behind the curve in terms of quantitative hockey analysis or they are purposely misdirecting Cazeneuve because they don’t want to share any secrets (or some mix therein). The latter possibility is hinted at in the piece by Doug Wilson, who cheekily offers a “no comment” to the question of whether the Sharks track possession or not.

If it’s the former, however, then I’m pretty confused. As mentioned, there’s a vast body of on-going research on possession that is growing and widely published on the web for free. At this point, NHL executives and GM’s would have to be either purposefully ignorant of this research or so isolated in their organizations that they are woefully unaware of anything beyond their own borders.

If it seems unlikely that a bunch of outsiders and amateurs would be a step ahead of hockey’s higher-ups when it comes to something this fundamental, but take another look at Holland’s quote at the opening of this post. He mentions the Oakland A’s Billy Beane and his reliance on new stats* (including on-base percentage) to find efficiencies in baseball markets in order to compete. What goes unsaid is the fact that Beane was actually standing on the shoulders of Bill James, the father of baseball Sabremetics who was both an amateur and an outsider himself.

Nobody in the league can agree on just how to quantify puck possession. But everybody knows that hockey’s most elusive statistic is essential to winning the Stanley Cup.

So says the subheading of the Cazeneuve piece. He’s only half right.

*(Beane’s discovery of and reliance on Jamesian “new stats”, of course, was the basis for the well-known Michael Lewis book Moneyball which I highly recommend, even if you have no interest in baseball itself)

Comments (17)

  1. Given the fact that these stats were tracked by the coaches in the Summit Series in 1972 I suspect that he is being a little coy here.

  2. Considering how much noise exists in stats like this, the teams absolutely use proprietary metrics and aren’t about to share.

    Not unlike the various methods NBA teams calculate defensive value and/or plus minus.

  3. I’m still on the fence as to how well Corsi correlates to actual puck possession. Maybe I’m out to lunch, but Corsi tracks too much of the effect and not enough of the cause in my book.

  4. We absolutely know that teams are tracking this information and Holland is being coy. Too many conversations between stat geeks and NHL execs have occurred to think otherwise.

  5. Skeeter, how can you be “on the fence” about correlation? It’s a number! Are you on the fence about whether the number six is actually a number?

    Puck possession = % of passes = Fenwick = Corsi = Scoring Chances. You can read the details on a bunch of different sites. NHL coaches and GMs track all of this stuff in one way or another.

  6. Teams track this stuff, no doubt. How much they weight it from team to team and how they apply the information would be really interesting to find out.

    Brian Burke seemed unconvinced when he was asked about Sabremetrics in hockey by Bill Simmons. I was always under the impression that he was a big proponent of advanced stats, but again, he could be guarding the “secrets” like Holland and Wilson.

  7. If it seems unlikely that a bunch of outsiders and amateurs would be a step ahead of hockey’s higher-ups when it comes to something this fundamental

    Very unlikely. And if it were true, then isn’t that the real story?

    Kent Wilson Knows More About Puck Possession Than Anyone in the Detroit Red Wings Organization. <– Now there's your story!

  8. @Hawerchuk

    Yes, it’s just a number. A number that I’m not sure correlates 1:1 with puck possession. That’s all.

  9. It may be that league decision-makers are reluctant to use a metric based on the high correlation between Corsi and scoring chances, because the high correlation takes place in an incentive environment where teams and players are trying to outscore (or out-scoring chance, which is pretty close). If teams start using Corsi as an evaluation tool, the correlation may drop as a result of changing incentives, where players and teams try to out-Corsi the opposition instead of outscore the opposition.

    This is not a problem that outsiders on the internet need to consider, just the decision-makers.

  10. Skeeter

    So what’s your point? You don’t think A and B are equivalent. And? What’s your solution then? What alternate theories of the crime do you have to offer?

  11. [...] we released the hounds (Kent Wilson) on an article by Brian Cazeneuve at Sports Illustrated. Kent took issue with the absence of any mention of puck possession stats (i.e. Corsi) in an article about the [...]

  12. Brian Burke seemed unconvinced when he was asked about Sabremetrics in hockey by Bill Simmons. I was always under the impression that he was a big proponent of advanced stats, but again, he could be guarding the “secrets” like Holland and Wilson.

    Burke tracks a plethora of advanced stats

  13. Bruce Dowbiggin makes an interesting point in “Money Players” about how the NHLPA started using statistics like blocks or hits in arbitration hearings to make middle-of-the-road players look much better statistically. Maybe that’s why GMs aren’t upfront about tracking puck possession…it’s a pretty big deal given current league trends, and if players up for arbitration can use that as a way to get more money, the GMs definitely don’t want the NHLPA using it as an official stat.

  14. Everyone agrees that Corsi is useful, but few people agree it’s anything close to the magic bullet that OBP was.. OBP is a direct individual measure of a valuable output. You can’t fake it, if you’re getting on base that often, that really is exactly what the GM wants out of you. Corsi isn’t a measure of a good outcome, it’s just a proxy for one that depends heavily on the performance of the other people who are on ice with you.. It statistically TENDS to correlate with good things happening, but it isn’t itself per se the good thing. And there are some ways of trying to statistically filter out the impact of teammates, but those are also imperfect and not everyone agrees on those.

    I think this is what Holland met

    (that, and as others point out, a GM saying “we value Corsi” is just ASKING for his players to start gaming the system, firing shots every time they’re in the Ozone, no matter if the goalie is unscreened, set, and staring them down over 30 feet of empty space, or is totally blocked off. You can rack up a LOT of useless shots if you know that your paycheck depends on it.

  15. Fantastic point by Overpass. It is one I agree with 100% and makes all too much sense in this circumstance as a reason to not make that the “goal”

    Additionally, no other counting stat is so easy to achieve a success in as corsi, as players have tons of times throughout a game where they can just throw pucks towards the net and no one can really stop them. Even a metric like shots is not so cited in “stat” circles

  16. Additionally, no other counting stat is so easy to achieve a success in as corsi,

    What evidence can you offer that it’s easy to achieve success in Corsi?

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