“Zone-adjusted Corsi” and the Magnificent John-Michael Liles
By Cam Charron
11 years ago
I don’t necessarily intend to use this space to write savage things about Jake Gardiner, but due to the limited number of young Toronto Maple Leafs’ defencemen who can potentially crack a major league roster this season, expectations may be too high for the kid.
Grading offence isn’t too hard to do. Usually, you can look at a player’s goal totals and determine how good they are in the offensive zone. Defence is a little more suspect, however. How can you grade how good a player is defensively? You could use many things, to how many minutes a player is used on defence, or in what role a player is used by who his coach matches him up against.
It doesn’t give you an exact answer, though. How good is somebody like, say, Jake Gardiner at playing defence? How successful does he, or will, he, make the Leafs?
Something statisticians, and now a growing number of online hockey writers, have been using is what’s called a “Corsi” number. Corsi acts like plus/minus, with some differences. Here’s an old post which goes through the basics:
Let’s start with a simple definition. “Corsi” is the difference between all shots directed at net for and against at even strength. That is (shots+blocked shots+goals+missed shots FOR – SH+BLK+G+MS AGAINST). The purpose of the stat is to determine possession. It is, in fact, a proxy for “zone time”. A positive corsi rate = more offensive zone time. Negative = more defensive zone time.Here’s an analogy that might help. Let’s say a hockey game is a tug of war. Corsi is the how far right or left of center the rope is. On an individual level, it’s an expression of which players are really pulling the rope. Therefore, if your team has a positive corsi rate, it means they are spending more time in the offensive zone at even stregth. It means they are pulling the rope harder than the opposition.
Corsi is tracked at a website called BehindTheNet.ca, but unfortunately, you can’t just look at a player’s Corsi number to determine his importance. It’s an elephant gun, however. It’s powerful, but imprecise. The reason shots are used is because there’s far less variability year to year between shots than goals, so Corsi has a better predictive value than simple plus/minus.
Behind The Net calculates other important aspects of the game, such as which zone a player is more likely to start his shift. Obviously, players who start regularly in the defensive end are more likely to have a worse Corsi number.
Another thing it does is average the Corsi rate of opposing skaters to determine a player’s quality of competition mark.
Using these three concepts, we can answer certain questions about Toronto’s defence, and how successful they’ll be next season.
By accounting for the number of times a player started a shift in the defensive or offensive zone, I’ve adjusted the Corsi rates for the Leafs defence in an effort to answer questions about Gardiner, Mike Komisarek, and John-Michael Liles, the players that will mostly make up the Leafs’ second pairing if nothing else changes. What is the best option for the Leafs to use if they want to continuously push play to the other end of the ice?
Well, this is what I found. “ZAC” is an acronym I use for “Zone-adjusted Corsi”. It’s a per 60 minutes rate. “Rel QoC” is the quality of competition faced by each player. Alongside the two, I looked at on-ice goals for and goals against per 60 minutes of each player to give us some indication of whether the player’s plus/minus total synced up with Corsi.
Obviously, there are some surprises here. The Leafs gave up more goals with Jake Gardiner on the ice than anybody but Komisarek or the new Philadelphia Flyer Luke Schenn. Despite facing the second easiest competition on the Leafs, the team was hemmed in their own zone with Gardiner on the ice.
At the top, it’s also surprising. Liles and Komisarek didn’t play the tough minutes than Dion Phaneuf and Carl Gunnarsson played, but they were effective at moving the puck given their role. I think the Leafs need another guy in the top four who can play a plus Corsi game against decent competition, but I think it’s clear that, if the season were to start tomorrow, Liles and Komisarek would be the second pairing.
As for Gardiner, there’s still room to grow. He’s an impressive skater with tuned offensive instincts. He needs to improve on his neutral zone play before the Leafs can be expected him to carry much of a load minutes-wise. The other thing is that Jay Rosehill should probably not play another game in the NHL, ever.
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