USA Today published an article on Thursday that describes the skeptical attitude many in hockey’s orthodoxy have towards puck possession statistics. The Corsi denialism movement, as described by Kevin Allen, is noteworthy for two reasons:
- It is articulated by Washington Capitals head coach Barry Trotz, and
- It is not correct.
It’s understandable why people might mistrust advanced stats, but these arguments don’t survive a closer look.
Super-fast crash course: Corsi is shot-attempt differential. If your team attempts more shots than your opponent’s team when you’re on the ice, congrats, you’ve got a higher Corsi. That’s good. Corsi is a proxy for puck possession, and it helps us better predict future goal differential.
Robust peer review has been trying to poke holes or at least quantify the limitations of Corsi for nearly a decade, so the notion of a player “gaming” the system by taking more low quality shots is not new.
But here’s the latest criticism, as described by Allen:
Take a shot on goal, from anywhere on the ice, even if your team is struggling to move the puck into the offensive zone, and it will help your Corsi.
And Barry Trotz’s continuation:
“They don’t get a scoring opportunity and we get the puck back, and all five of my guys get a minus because a guy makes a poor play at the red line,” Trotz said. “Plus, he and his teammates get rewarded for that.”
This idea represents an incomplete understanding of how puck possession is calculated and how it works.
Your team’s shot-attempt differential will indeed go up if you make a shot attempt, but we should also consider that:
- Your team’s shot attempts are only half of the equation for puck possession. If your shot attempt is followed by one or more opponent shot attempts, it will not improve your Corsi.
- A shot on goal from outside the offensive zone has no sustained pressure, so it will likely lead to a turnover, which is more likely to lead to opponent shot attempts.
- If a shot from 25 feet behind the blue line misses the net, it will result in icing, which leads to a defensive zone face-off, which is more likely to lead to opponent shot attempts.
While Corsi explicitly measures shot attempts, shot-attempt differentials themselves are the result of underlying performances that are more complicated than just “pulling the trigger.”
Taking distant, low-quality shots might lead to a momentary increase in Corsi, but it will not last. There will be fewer follow-up shots, the opponent will get the puck back, and now you’re playing defense.
The following are important skills for being a good Corsi player:
- Gaining the offensive zone with possession.
- Creating opportunities for shots.
- Getting rebounds and secondary chances.
- Disrupting the opponent’s attack.
These are also important skills for being a good Overall player.
I can’t believe I have to say this, but there is more to hockey than possession. Literally no one argues otherwise. Qualitative analysis, sorry, I mean, the eyeball test, is indispensable for connecting the how (tactics) to the what (possession).
If there are “businessmen” in the league who inflate their possession by taking superfluous low-quality shots, I’d be surprised. I’d be surprised if the humans who record shot attempts routinely count garbage shots from outside the offensive zone, and I’d be surprised if the behavior of those players actually led to an improved shot-attempt differential.
But I’m certainly curious. I’d encourage curiosity for everyone who is skeptical about possession stats too. If you’d like to know more, there are lots of smart people who study this stuff. In my experience they’re both considerate of dissenting perspectives and inordinately gracious with their research. A few examples:
And also please feel free to harass Pat Holden at any time about any topic, whether “gaming” Corsi or TJ Oshie’s goal-scoring pace.
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