Duncan Keith was just trying to make a joke.
But in doing so, he raised an interesting point about the merits and shortfalls of hockey’s proxy stats.
First, some context: Keith has visibly made an effort to shoot the puck more often recently. Blackhawks coach Jeremy Colliton noted it Sunday, and the data backs him up.
Keith attempted five shots in the Hawks’ first game against the Blue Jackets, then 10 in the second game — leading the team with six on goal — despite averaging just 2.3 attempts per game previously.
There’s a real reason why, too.
“It started on the power play,” Keith said Monday. “We didn’t really have too much [going], a couple entries didn’t work out, and I just figured that we needed to start getting some shots. I shot a few and we were able to get a little momentum, and then a few other things opened up… It’s important that if I have the shot there, I have to use it.”
But before giving that thorough answer, Keith made a quip that went viral in the hockey world and ignited a years-old argument on Twitter, Reddit and beyond:
“Getting the Corsi up so you guys think I’m good.”
Duncan Keith on his many shot attempts the past 2 games: “Getting the Corsi up so you guys think I’m good.”
— Ben Pope (@BenPopeCST) February 1, 2021
Corsi, of course, is the statistic that uses the ratio of shot attempts taken by a player’s team, and by his opponent, during his ice time as an evaluator of his performance. It’s purely quantity-based.
In recent years, analysts have somewhat shifted away from Corsi and instead toward scoring chances — the stat frequently referenced in this newspaper’s Hawks coverage — and the more-complex “expected goals.” Those stats incorporate both quantity and quality and thus give a more accurate, comprehensive evaluation of performance.
Yet Corsi remains the buzzword for the entire family of statistics, making it both the most well-recognized and the most contentious.
Keith is far from the first NHL player ever to criticize Corsi for its overuse. Fellow Hawks defenseman Calvin de Haan memorably did the same thing last season in a far longer, more in-depth rant. (De Haan chimed in again Monday, tweeting “Dunks isn’t wrong.”)
Keith is, however, perhaps the first NHL player to imply — even clearly jokingly — that a desire to maximize Corsi could theoretically affect decisions on the ice.
That brings up the philosophical maxim colloquially called Goodhart’s Law: “When a measure becomes a target, it ceases to be a good measure.”
It would certainly be possible for an NHL player to slightly manipulate Corsi if he so wished.
Consider he had the puck on the perimeter of the offensive zone. He could either shoot, minutely improving his Corsi ratio but with almost no chance of scoring, or make a pass, foregoing the guaranteed shot attempt but potentially leading to a better scoring opportunity in the future.
And while there’s no documented evidence of a player actually, consciously manipulating his Corsi, there would be plausible motivation.
Corsi and other similarly “advanced” stats are often brought up in contract negotiations — and players are keenly aware of which stats are and aren’t, as Nikita Zadorov evidenced Monday when told he ranked top-five in hits per game.
“I don’t think that stat’s going to…give an extra $5 million,” Zadorov joked. “It’s not points or goals or anything.”
Therein lies Corsi’s problem.
As a proxy for possession rate, it has definite value, at least until the NHL’s new player- and puck-tracking data becomes publicly available. But the data points that serve as its foundation — shot attempts — are not, depending on context, always valuable themselves.
Conversely, there’s no question scoring chances are always valuable. A player who “manipulated” his scoring-chance ratio would have simply become a better player — the very thing proxy statistics intend to measure.
Keith probably didn’t think about any of that Monday. But his viral quip raised a good point nonetheless.