On Corsi and Faceoffs
I’m fairly skeptical of much of the statistical analysis being kicked around these days. I accept that hockey is a clash of probabilities and that events come more or less randomly. That makes statistical analysis possible, but I think all of the efforts to apply them to improve our assessment of individuals fail, partly because the sample size is always small and more importantly because individual numbers are always hopelessly polluted by the team context.
I don’t really object if someone tries to squeeze something interesting from the numbers, but I don’t take them very seriously either. Greg Ballentine likes Corsi rankings enough that he devotes three recent posts to them. In one, he notes that Ryan Kesler improved from 35th to 1st in the league standings, largely because his role changed when Manny Malhotra was signed. In another, he explains why Ryan Clowe finished second to Kesler last season. And finally, Greg explains how the statistic clearly shows that Saku Koivu was really bad last year.
Greg’s examples, it seems to me, make a good case against the Corsi statistic. First, both the Kesler and Clowe stories tell us how much influence context has – neither Kesler nor Clowe could have done it playing on a different team or even playing in a different role on the same team. In other words, this is not really an individual statistic. Second, while Ryan Clowe is a very good player, any statistic that ranks him as the second best player has some credibility problems. Greg explains it, but explanations can’t compensate for a number that ranks Ryan Clowe as one of the best players in the league. Third, does the number fill a real need? I don’t think we need a Corsi number to know that Koivu’s game has fallen off a cliff.
On the other hand, I really like the kind of statistical analysis Tyler Dellow does in this piece. He tests a common claim – that faceoffs are important on special teams – by using relatively reliable team level data. He presents the evidence well and I think the conclusion – that faceoffs aren’t that important – is compelling.
Finally, Tyler’s study has a practical application applies the conclusion to a choice the Oilers have on the power play next season. He thinks it would be fine to go without a natural centre on the first power play unit. (I agree. I don’t think the Canucks were hurt because the second unit power play didn’t have a centre for much of the season.)
That the conclusion jibes with a position I’ve held for a long time does not surprise me but that’s not really why I liked the post. If the data had shown that the faceoff was important, I would have had to reconsider my position.
Tyler and I do disagree on one point. When explaining why winning the first faceoff is insignificant, Tyler writes:
I’ve put some thought into why the difference might be so small and the answer that I’ve come up with is that, when you’re facing an elite PP team, whether you win the draw or lose the draw, you’re going to have to taste the poison. If you lose the draw, they get to set up and throw their best at you for a minute and a little more, subject to any clears. If you win the draw and ice the puck, what happens?
The reason the difference is small is because it is a game of puck position, not puck possession. Whether you win or lose the draw, the puck is deep in their end and you have an extra man. We mash together the words “win the draw and ice the puck”. Those are two separate things and the easier part by far is winning the draw.
Generally, a defenceman hurries back while the forwards take a leisurely skate back to the red line or far blue line. They aren’t hard seconds to play. It would be interesting to take a look at the average shift length on the PP for stars in shifts where they won the initial faceoff versus those where they lost. I strongly suspect we’d find that the shifts tend to be longer when they’ve lost the initial faceoff.
If the penalty kill wins the draw and clears the puck, it is a very good thing. A good PK will harass the puck the entire 200 feet back. If the power play can’t get set up, it won’t score often.