I’ve been rolling around this problem with the offensive zone faceoff losses and the 2013-14 Oilers in my brain for the past few days, trying to work it out. The problem is probably best summed up in a graph from this post:
In a nutshell, the problem is “Why did they become terrible following OZ faceoff losses after December 7?” The change is so stark that there has to be a reason for it. I had a sneaking suspicion that it might have something to do with the Oilers trying to win more offensive zone faceoffs, so I decided to put together a graph with two things: their 5v5 offensive zone faceoff winning percentage over the season and their Corsi% following OZ faceoff losses.
Huh. So the OZ- Corsi% went down as the OZ faceoff winning percentage went up. Is it possible that those two things are related?
The way in which I’ve been looking at and talking about post-OZ faceoffs has been a bit artificial. I’ve been suggesting that tactics play a big role in the outcome when you lose a draw. The artificial part is that when a coach is choosing the plays and tactics that his players are going to employ, he doesn’t know whether the faceoff will be won or lost.
It’s not unlike blackjack, in the coach wants to make the decision that has the best expected value in the face of unknowns. In blackjack, the player knows what his cards are but he doesn’t know what the dealer has or what the next card out of the shoe will be. He has to make his decisions with an eye towards maximizing his value based on the probability of various unknown outcomes.
A hockey coach needs to maximize his value by choosing the tactics that maximize the expected goal difference. Goals are rare in hockey, so we use Corsi% and, for the time being, trust that the goals for/against will take of themselves. There’s basically a two step process here that determines the value that you’re getting following faceoffs. The first, obviously, is whether you win the bloody thing. Once you’ve won or lost the faceoff, it’s then a question of how good you are at generating Corsi% out of that situation.
The twist, which doesn’t really exist in blackjack, is that you can alter the likelihood of winning the faceoff by the decisions that you make about how your team approaches the faceoff. What’s more, how you approach the faceoff can then impact on the Corsi% that you’re going to generate post-faceoff.
Basically, it’s an equation for the coach to maximize:1+((Probability of losing the faceoff)*(Corsi% post-faceoff loss)) = faceoff Corsi%. There’s a weighting issue to take into account – there are going to be fewer Corsi events in period X following an OZ faceoff loss than there will be in the same period following an OZ faceoff win – but don’t worry about it. This is the technical side of what the coach has to do.
I hate when these things get too abstract, so let’s talk about the Oilers here. I’ve been using December 7 as my sort of date when it all changed since I got talking about the Oilers and OZ faceoff losses. Essentially, my working theory has been that something changed in terms of how they approached the faceoffs, resulting in their Corsi% falling apart. I might not have the date exactly right – it could be a bit before or after that – but I think it’s somewhere around there.
Here’s what the pre and post December 7 OZ faceoff numbers look like for the Oilers.
Boy, there are a lot of names in there. You know what? I can summarize this. Let’s do it this way:
That kind of highlights what happened, eh? Gagner and Nugent-Hopkins were helpless on 5v5 offensive zone faceoffs right up until December 7. After December 7 (Game 31), they were as good as the rest of the team put together was at offensive zone faceoffs was. Seems a belter of a coincidence that they both got a lot better at the same time. I’ve graphed their OZ faceoff winning percentage as the season went along, which you can see here – they improve in lockstep:
It seems strange to me that they would both learn how to win faceoffs at exactly the same time. When I happened across this, I was reminded of a Craig MacTavish press conference at the end of last season. MacT was asked about Gagner’s trouble on the dot and he said this:
Apparently from the analytics people, every 40 faceoffs that you lose in the defensive zone, one will end up in your net in the next 30 seconds, so it’s valuable but there are ways you can help support a centreman who has trouble winning faceoffs.
Winning faceoffs is just part of the equation though. We care about faceoffs because possession of the puck means that you’re more likely to generate Corsi% (and, by extension, goals) than the other guy. We know that, in general, winning faceoffs means that you get a Corsi% boost overall. We would not, however, want to employ a strategy that resulted in us winning more faceoffs if it resulted in a net reduction of our Corsi%.
Is it possible that the Oilers employed a strategy to try and prop up Gagner and RNH’s abysmal OZ faceoff numbers that a) increased their winning percentage on offensive zone faceoffs and b) resulted in an overall net reduction in the Corsi% that the Oilers were generating following offensive zone faceoffs? Amazingly, I kind of suspect that the answer to this is a) yes, it’s possible and b) yes, it happened.
When I measure Corsi% post-faceoff, I have different lengths of time for which I measure it, depending on the outcome of the faceoff. Different outcomes and locations of the draw result in effects for different lengths of time on average. Win an offensive zone faceoff at 5v5, the effect is visible for 37 seconds in the data. For offensive zone losses, it’s visible for 21 seconds.
If I want to look at how a team did after offensive zone faceoffs overall, I need a standardized length of time. To do this, I just counted all events within 37 seconds of an offensive zone faceoff, regardless of whether it was won or lost. The question that I am asking becomes this: did the Oilers do markedly worse following offensive zone faceoffs post December 7 despite a significant increase in their team OZ faceoff percentage because of the improvement from Gagner and RNH?
Well that’s disheartening. Like Jesus said, what shall it profit a centre if he wins 100% of his faceoffs but his Corsi% goes down?
I can split this out a little bit more and break it down by wins and losses. I’m going to do the losses first, because I have a bit more of a nuanced point to make about the wins.
We already knew that the Oilers got really bad following offensive zone losses post December 7, so there’s nothing new here. Obviously, this is a big part of the reason for their overall decline in Corsi% following offensive zone faceoffs – even though they reduced their lost faceoffs from 56.1% to 50.9%, they dropped 18 points of Corsi following losses.
What’s going on here is a little more subtle. There’s a decline in Corsi%, enough to make the Oilers a pretty ineffectual team when they won an offensive zone faceoff at 5v5 over the last 51 games of the year – that 68.6% figure stinks when you’re starting with the puck in the opposition’s end. The interesting thing is the why – the rate at which they allow shot attempts following offensive zone faceoff wins actually declined, from 0.323 shot attempts per OZ faceoff win to 0.292. The rate at which they generated shots following OZ faceoff wins plummeted, from 0.848 to 0.646.
Two final factbombs for this piece, which is already too long but I sort of had one of those moments where you see the whole horse, so I figured I wouldn’t parcel it out and I’m prone to parentheticals which up the word count so here we are. The Oilers basically had three guys who did all of the offensive zone faceoff work: Gagner, RNH and Boyd Gordon. Gordon’s kind of the opposite of Gagner and RNH in that he basically has no offensive skill to speak of but he can win faceoffs without a lot of help.
If you were a hockey coach who was designing something to help out your guys on offensive zone faceoffs, you wouldn’t necessarily involve Gordon – he doesn’t really need the help. Sure enough, we saw in the stats for offensive zone faceoff wins pre and post December 7 that Gordon’s number just basically stayed the same while Gagner and RNH saw dramatic improvements.
If that’s the case and we’re suspicious that there was a change to faceoff tactics that hurt the Oilers Corsi% following offensive zone faceoffs, we wouldn’t necessarily think that it would show up with Gordon on the ice. You don’t need to fix things that aren’t broken. We might therefore suspect that Gordon’s Corsi% following offensive zone faceoffs would be pretty much unchanged pre and post December 7, while Gagner and RNH saw big declines.
Yep. The drop for Gordon is insignificant – it’s one Corsi event going the other way. The drop for Gagner and RNH is massive. All of the decline is focused around them, which is consistent with my theory that the Oilers were doing something to try and help them out and it backfired badly.
Final question: does any of this have any significant effect? I’m inclined to think that the answer to this is yes. The Oilers generated 1784 shot attempts this year and allowed 2323. If we assume that the Oilers could have carried on exactly as they had prior to December 7, with a lower faceoff winning percentage but a higher Corsi% off offensive zone faceoffs, that gives us a 44.8% Corsi% for the year instead of 43.4%. Some back of the envelope math tells us suggests that’s worth 4 or 5 goal difference. That’s a conservative estimate as well – more shot attempts likely has some knock-on effects.
To sum it all up, the data shows us that the Oilers became far less successful in terms of Corsi% following 5v5 offensive zone faceoffs as the season wore on, despite winning more of those faceoffs. The improvement in winning faceoffs came from two players: RNH and Sam Gagner. The other centre, who didn’t have a big improvement in his faceoff winning percentage, saw his Corsi% following offensive zone faceoffs stay essentially the same. Gagner and RNH cratered. It seems reasonable to suspect that the Oilers changed their approach to offensive zone faceoffs in a successful effort to improve the numbers when Gagner and RNH were on the ice and that this succeeded in improving the statistic which shows up on the gamesheet each night, while undermining a far more important one that doesn’t.Email Tyler Dellow at email@example.com
- Probability of winning the faceoff)*(Corsi% post-faceoff win [↩]