TSN’s Ryan Rishaug did an interview with Taylor Hall that TSN aired before the Oilers game in Minnesota. It was pretty interesting for a couple of reasons. First, it’s still kind of weird to see a hockey player dropping Corsi and Fenwick correctly in an interview. Hall made what I consider to be an entirely correct observation about the challenge that teams will have with turning data into things that are actionable:
Whether they’re useful or not (referring to data or, to use the phrase I hate “advanced stats”), I do think they are for sure, but the thing for a hockey player, if you’re an advanced stat guy and you’re describing to a hockey player, you have to have like some kind of end point. Like, what does he have to do better to get this stat better. That’s the thing that I’m lost on, with Corsi and Fenwick and all this stuff, how do you improve a player by it, what do you tell him?
That’s sort of what I’ve been hung up on for the past year, thinking about how to do that. It was another comment that he made that I want to poke into a bit though. Rishaug asked him about his Corsi% this year and this exchange ensued.
Hall: This year my Corsi hasn’t been as good as last year.
Rishaug: And does that make sense to you based on your play, does that add up?
Hall: It doesn’t, no. But my chances, for and against, are about the same as last year. So what that means, I’m not really sure. I know we have an advanced stat guy that does it all for our team and I asked him, I said ‘So why’s my Corsi not as good?’ and he really didn’t have an answer for me.
In all fairness to the Oilers stats guy, it’s a hard question – I’ve fiddled with it a fair bit and I have some theories, some ideas, but not much more than that. It’s a question that’s answerable with data, I think, but the data doesn’t exist to do it. Someone needs to generate it. I imagine some teams do and more will in the near future.
It’s the bit about the scoring chances that really caught my attention though. Hall doesn’t really explain the statement and, in particular, whether he’s talking about the chances when he’s on the ice or whether the Oilers have a metric like Neilson Numbers. Neilson Numbers essentially involve assigning credit/blame for scoring chances for or against. The problem with them is that they don’t credit a player who creates the context, say by breaking a cycle in his own end, or making a quick outlet pass. Taylor Hall’s going to have way better Neilson Numbers with Brian Campbell and Jeff Petry behind him than he’d have with me and Dennis King. Basically, Neilson Numbers suffer from the same flaw as Corsi% does; they just pretend to deal with it by discarding information.
David Staples has counted scoring chances for the Oilers over the past few years. Unfortunately, he doesn’t present the time stamped information that would let us see whether the totals when Hall’s on the ice have changed. He does, however, present totals. In 2012-13, according to Staples, the Oilers got 44.9% of the ES chances. They had a 44.5% Corsi%. This year, the Oilers have had 46.6% of the ES chances and they’ve got a Corsi% of 44.6%. So they’re getting a few more of the chances but not that many.
Keep in mind that Corsi% is generally presented solely on the basis of 5v5 data – that’s what I’ve used here. Staples’ data is ES, which I assume includes 4v4. I’d guess that that accounts for some of the difference – the Oilers have been a much better 4v4 team this year. Overall though, the scoring chances seem to track the Corsi% pretty well, which is what we’d expect given what Eric Tulsky’s found in the past.
What if we look at Hall’s Neilson Numbers? While they’re not particularly helpful data, they do give us a sense of how many scoring chances Hall was on the ice for, assuming Hall’s rate of contribution to scoring chances remained the same. Staples calculates these on the basis of contributions to scoring chances per 15 minutes. We’ll contrast that with the number of shot attempts for and shot attempts against that he’s been on the ice for per 20 minutes, just to see if the change is similar.
The decline in contribution to scoring chances is basically bang on with the decline in the shot attempt rate when he’s out there. According to Staples, he’s contributing to scoring chances at about 80% of the rate he did last year; the Oilers are getting shot attempts with him on the ice at about 83% of the rate that they did last year. The increase in the scoring chance against rate is way higher than the increase in the shot attempts against when he’s on the ice, which is sort of odd.
If Hall was talking about the overall numbers and intending to convey that the Oilers get about the same chances for and against when he’s on the ice this year and last, and Staples is accurately tracking who makes the play or mistake that leads to the scoring chance (and I don’t really take issue with his ability to do so, subject to some limitations in terms of knowing the Oilers systems that any outsider has), then it means Hall is contributing less frequently to scoring chances and making more mistakes on scoring chances. That seems really unlikely to me. I’m inclined to think that there has been some sort of negative change in the scoring chances when he’s on the ice.
There’s a point that I possibly haven’t made clear enough: I’ve written a lot about it being a problem when Hall’s on the ice. That doesn’t necessarily mean it’s a problem with Hall – it could be something else entirely that’s resulting in the puck being on his stick with an opportunity to make a play less often. I don’t think that this is the issue but if, for example, you stuck Hall with four guys like me, his Corsi% would crater but it would be nothing to do with him.
One other point: it’s not just Hall’s Corsi% that’s dropped off, the goal for/against ratio when he’s on the ice has fallen off too. Last year, the Oilers got 53.8% of the goals when he was on the ice at 5v5. This year, it’s 47.4% of the goals when he’s on the ice. His on-ice shooting percentage and on-ice save percentage are virtually unchanged – this isn’t a case of bad luck. If he’s getting the same volume of chances for and against when he’s on the ice, then the opposition must be scoring on way more of their chances this year and the Oilers must be scoring on fewer of theirs, with the opposition adding a bunch of low risk shots and the Oilers not getting many of them. This doesn’t really make sense to me as an explanation and yet, it would have to be true if Hall’s right about the scoring chances.
In any event, his broader point is accurate – there has to be an end point, some sort of identification of X, Y and Z that has changed for the information to be actionable. At present, it’s good for providing direction as to where things are going wrong/right. I’ve no doubt that the Oilers will figure it out, or that they have and it’s a short term pain for long term gain kind of thing. When data gathering takes the next step – which I firmly believe it will – this sort of thing should become much easier to tackle.
Update:: The indispensable Young Willis notes on Twitter that he has been tracking scoring chances based on who’s on the ice. Last year, he had the Oilers getting 52.7% of the 5v5 chances when Hall’s on the ice. This year? 47.6%.Email Tyler Dellow at firstname.lastname@example.org