I have, over the past couple years, increasingly come to be of the view that the value of a defenceman at 5v5 lies in how he affects his team’s Corsi%. There’s no real magic to this conclusion – once you conclude that defencemen have a negligible impact on the save percentage and shooting percentage when they’re on the ice at 5v5, this is all you’re left with.1
The question is then this: how do we do any evaluation of a defenceman by way of Corsi%? We know that it’s fraught with problems. Most obviously, some guys play on good teams and some guys don’t play on good teams. I’ve suspected for a long time that the league, as a whole, doesn’t do a very good job of dealing with defencemen who play on bad teams unless it’s painfully obvious that they’re really good but being held back. Even then, these guys tend to get tagged as being problems.
The intuitive way to go about doing this is to look at CorsiRel, which looks at how a player’s team does with and without him on the ice. When I write about guys like Tom Gilbert and Anton Stralman, the basic premise of my argument is pretty much always that they seem to make things better when they’re on the ice. Players like that should be players that you want because they make your team better.
I’ve never seen anyone explicitly test this – it sounds logical, but does it work? In order to take a look, I set out to identify guys who were top four defencemen who played an entire season with one team and then an entire season with another team. I set cutoffs for each year of 41 games played and 19 minutes a night of ice time. I discarded Dustin Bufuglien and Brent Burns, just because of the positional issues. This gave me a list of 50 defencemen who played complete seasons with one team and the next year played a complete season with another.
A word about CorsiRel. There is probably a difference between a guy who posts +5.0% CorsiRel on a team that puts up a 40% Corsi when he’s not on the ice and a guy who posts a +5.0% CorsiRel on a team that puts up a 60% Corsi when he’s not on the ice. It’s harder to make a really good team better than it is to make a really bad team better. My suspicion is that, all other things being equal, CorsiRel works something like this:
Don’t get hung up on the numbers in that graph – they’re just to illustrate a point. Basically, what I’m saying is that a rising tide lifts all boats but, unlike with tides and boats, with defenceman and Corsi, the rising tide will lift a defenceman but the higher the tide, the lower he sits in the water.
OK. Let’s take a look at the guys who had a year one CorsiRel of at least +1.5% – guys who made their team better when they were on the ice. Did that continue in the second year?
(Note: the “Corsi%” column refers to the team’s Corsi% when the player is not on the ice. To get his Corsi%, you just add or subtract as necessary.)
In ten out of twelve cases, it did continue in the second year. Only Kyle Quincey and Ryan Suter weren’t positive CorsiRel guys on their new teams although, in Suter’s case, he was playing on a team that posted better Corsi and without Shea Weber as a defensive partner. I suspect, although I can’t be certain, that Colorado tried Quincey as a first pairing defenceman, which was probably a step up in terms of competition from his year in LA. Overall though, it holds pretty well.
What if we look at the other side of the coin – guys who had a CorsiRel of at least -1.5% in Year One and then moved to another team?
12 out of 16 were negative CorsiRel guys on their new teams. Of the four who weren’t, three of them (McCabe, Hamrlik and Ballard) went from decent possession teams to bad teams – it’s easier to look good on a bad team.
So the theory – such as it is – seems to roughly hold. This doesn’t mean that I’d endorse picking guys off CorsiRel alone – there are too many confounding factors. I’d want to know, in particular, who a guy is playing with, who he’s playing against and where he’s starting on the ice. That’s why I plowed through some of that information with respect to Anton Stralman the other day. As the starting point on discussing a guy though, it seems pretty good to me.Email Tyler Dellow at email@example.com