Last week, Cam Charron wrote about the NHL’s counting problem here at Backhand Shelf, bemoaning the secrecy of NHL teams when it comes to advanced statistics. One part in particular, however, caught my eye when he talked about hockey’s “Aha!” moment when it comes to statistics.
There’s a reference in the Friedman piece to Craig MacTavish walking around looking for the “Aha!” moment when it comes to hockey analytics. I don’t think MacTavish has realized that half the hockey world is a step ahead of him in that regard. The “Aha!” moment comes when you realize that shots are a hell of a lot more predictive than goals for determining future events. As soon as you realize that hockey is a game between two teams trying to take shots on goal, I think the rest of it falls into place.
Cam isn’t really wrong, but this is also one of the biggest problems that people seem to have with so-called advanced statistics: they’re almost entirely reliant on counting shots. Corsi and Fenwick are both shot-based statistics that are pretty much the opposite of “advanced.” All they are is adding and subtracting shots. The more shots for your team and the fewer shots against, the better. Outshoot your opponent enough, particularly at the right time of the game (such as when the score is tied or within one goal), and you’ll win a lot more games than you lose.
If this seems like an incredibly simplistic view of hockey, that’s because it is. It’s also a completely inaccurate view of hockey. That isn’t to say that Corsi and Fenwick aren’t useful, because they certainly are. As Cam points out, shot-based analytics have impressive predictive power. But they also are coming at hockey from the completely wrong end.
I believe this is part of the reason why so many people are resistant to shot-based statistics. What matters is winning, winning requires goals, and a high volume of shots does not, strictly speaking, create goals. Shots are a by-product and not a cause.
When we talk about Corsi, we’re talking about a statistic that acts as a proxy for puck possession. Corsi is essentially a plus/minus statistic that includes all shots on goal, missed shots and blocked shots, using the simple logic that if your team is taking a shot, then they have the puck. The more shots of all types that your team takes, the better. Fenwick is essentially the same, but removes blocked shots from the equation.
These two statistics have proven to be very useful for analyzing teams more accurately. A team’s Fenwick percentage when the score is close or tied, for instance, is generally far more predictive of a team’s future results than their current results. The Los Angeles Kings seemed to surprise everyone but the advanced statistics crowd with their dominance in the playoffs: they had the fourth highest Fenwick Close in the league. Then there was the well-predicted slide by the Minnesota Wild from top of the Western Conference to out of the playoffs.
But there’s still something about saying that more shots is better that rankles. When you watch a game, low percentage shots with no chance of going in certainly don’t look like they’re helping a team win. A defenceman that constantly misses the net is infuriating. I’ve even had discussions with people who suggest that players could start gaming the system if they knew their coach or GM used Corsi by intentionally taking more low-quality shots instead of looking for a better scoring chance. When you watch a hockey game, you can see that not all shots are equal, but Corsi and Fenwick treat them as if they are.
You don’t go to a hockey game to see your team take a lot of shots; you go to see your team score goals.
So, does a higher volume of shots lead to more goals? Sort of. Shots ride a fine line between correlation and causation. After all, as the Great One said, “You miss 100% of the shots you don’t take.” You can’t score if you don’t shoot. But a missed or blocked shot, by definition, cannot directly cause a goal, though they may lead to one indirectly.
All of those shots, whether on goal, missed, or blocked, are a by-product of what a team is actually attempting to do. The result a team is looking for is goals and, to that end, a coach puts in place systems, tactics, and game plans in order to prevent scoring chances for their opponents and create scoring chances for themselves that will produce that result. The players then put those into action and, as a by-product, produce shots on goal, missed shots, and blocked shots.
We count shots not because they’re the result of the process, but because they’re the most numerous by-product of the process.
There simply aren’t enough actual goals scored to create a large enough sample size to analyse. Fortunately, shots end up correlating nicely with goals over time. Fenwick correlates incredibly closely to scoring chances, but this isn’t because shooting the puck a lot is the same as creating a scoring chance. It’s just that the same processes that aim to produce shot quality will also produce shot quantity.
A forward might take a low-percentage shot from the outside, hoping for a rebound that will create a better scoring chance. A defenceman will sometimes throw the puck at the net while under pressure simply to keep the play alive. A fourth liner will shoot the puck as soon as he crosses the opponent’s blue line in order to create an offensive zone faceoff for his team’s top line. A top-six forward will optimistically shoot from a bad angle at the end of his shift after not being able to create a better scoring chance. The pursuit of shot quality will inevitably lead to shot quantity.
It’s not enough to simply outshoot your opponent: every NHL team knows this. It’s why you’ll never see players trying to game their Corsi by taking low-quality chances. What matters is goals and you score goals by doing things that hockey traditionalists love — making a good first pass out of the defensive zone, winning puck battles, creating turnovers in the neutral zone, going hard to the net, cycling the puck down low, etc.
All of the little things that lead to goals and wins over the long-term, lead to shots in the short-term. It’s not that shots matter more than goals — they absolutely don’t — but the things that make a team good at scoring and preventing goals also happen to make them good at taking and preventing shots.
As a by-product of trying to score goals, you’ll produce all sorts of shots — on goal, missed, and blocked. And we’ll add them, subtract them, and use them to analyse how well you did in the aggregate at all those things hockey traditionalists love.