Last night on twitter I posted some GF%RelTM statistics which resulted in a number of comments but notably some from Stephen Burtch about how players cannot be blamed for GF% and is nothing more than a fancy +/- stat and how players can’t be blamed or given credit for things such as save percentage.
— Stephen Burtch (@SteveBurtch) September 26, 2014
It isn’t just Burtch that has this sentiment. In an article on ArcticIceHockey.com HappyCaraT writes that “+/- is a stat that is pure luck.” There has been a lot of bashing of +/-, some fair, some overblown, and the result is this kind of sentiment. To suggest that +/- or some similar stat is all luck and has no validity or usefulness is just silly. Yes +/- is heavily team driven but so is Corsi and nearly every other NHL statistic so that is no reason to toss it aside. You just have to take that into consideration and look at things like ‘Rel’ stats and WOWY analysis. Yes it is impacted by luck and randomness but given large enough sample sizes that is largely mitigated and given large enough sample sizes it is predictive of future performance.
Now, to address Burtch’s specific comment about on-ice save percentage I don’t understand why anyone believes players cannot influence it. I have written about this before but we know players can impact save percentage because score effects are real. When players are protecting a lead they give up more shots but they end up as goals at a smaller rate while presumably playing against the oppositions best offensive players who definitely have better shooting percentages overall. Luck doesn’t only happen when you are protecting a lead and bad luck doesn’t always happen when you are trailing.
Furthermore, in recent months the following have been discovered:
- Shots taken on the rush are more difficult shots resulting in higher shooting percentages.
- Based on the zone entry/exit work by Corey Sznajder we have seen that players and teams allow successful zone entries against (which essentially result in more rush shot opportunities) at different rates.
These two observations taken together implies that the players that are better at minimizing clean zone entries against effectively should be able to boost their goalies on-ice save percentage. Who was the best Leaf defenseman in terms of limiting successful zone entries against on the Leafs last season? Dion Phaneuf. Who on the Leafs had the best Save%RelTM last year? Gunnarsson, who played mostly with Phaneuf. Phaneuf was a close second. In fact, over the past 4 seasons Phaneuf’s Save%RelTM has been +1.3%, +1.8%, +1.6% and +2.1%. Pretty consistently good. Is it a coincidence that a defenseman who is good as limiting successful zone entries against is good at boosting their goalies save percentage? I suspect not.
Now, what about Polak. Well, he has been -1.7, -2.4, -0.7, and -1.1. Not so good. Robidas has been -3.1, -3.5, -0.6, and -2.1. Wow, look at that. It’s a trend, and not a good one. Should we be predicting a tougher season for Maple Leaf goalies? Probably so.
When I get more time (currently working on my new website where you’ll get access to these RelTM stats) I’ll do some more research into studying the connection between zone entries against and save percentage. Until then I think there is at least some good evidence to support that limiting zone entries against is a big factor in being able to boost your on-ice save percentage (as well as your goalies save percentage).
So, can we please get past the idea that a statistics like GF% or GF%RelTM has zero merit and that all hockey analytics must be done using Corsi or Fenwick? Are there special concerns that need to be considered with these statistics? Sure, but calling them irrelevant, all luck, and not useful is the kind of thinking is only going to limit progress in hockey analytics. Shot quality exists and its real. At both ends of the rink. To take hockey analytics to the next level we need to research it and understand it better, not continually minimize it.