There was a post at The Puck Stops Here that was excerpted in a thread at Hockey’s Future that I thought warranted a bit of comment, as it touched on mc79hockey fave Dan Heyda. I’m going to excerpt a rather large part of it but go read the whole thing:
It is clear that when Jan Hejda is on the ice, his team outscores their opponents. It is also clear that his team is outshot significantly in the process. The logical conclusion is that Hejda forces opponents to take bad shots instead of creating good offensive opportunities. This is consistent with observation of his play.
Hejda highlights a problem with Corsi. It does not distinguish between bad shots and good shots. A blocked low percentage shot counts the same as a goal. He is the most significant example of a player in the NHL who has successfully forced lots of bad shots in place of a lesser number of good shots as a defensive strategy. He is an example that shows that Corsi Numbers of defencemen with little offensive talent should be taken with a grain of salt – especially when they disagree with +/- ratings.
Jan Hejda is a good defenceman. His +/- shows that he is effective in limiting scoring when he is on the ice. The fact that he does this by forcing low percentage shots does not hurt his playing level. His Corsi is misleading. He is the best example of that in the NHL. It is reasonable to be skeptical of the Corsi Ratings of other defensive players with low offensive value. In cases where their Corsi Rating and +/- disagree, the +/- is more likely to be the meaningful one.
I enjoy The Puck Stops Here and thought that the author, whoever he might be, was doing the Lord’s work in the playoffs when he was trying to convince red clad heathens that Chris Osgood was not, in fact, some sort of a playoff force and Hall of Fame level talent. This post above strikes me as being just crazy though.
To start with, I don’t know how he concludes that Hejda was forcing low percentage shots. Maybe it’s true, maybe it’s not, but the Jackets had a shooting percentage of 10.4% when Hejda was on the ice last year and shot 8.0% when he wasn’t on the ice. I am likely amongst the 250 or so biggest Hejda fans in the world and if we were all assembled in one place, I don’t think that any of us would be crediting him with nudging the Jackets’ shooting percentage by 2.4 percentage points. If the Jackets shoot 8% with him on the ice, he falls from +14 at 5v5 to even (all stats courtesy of timeonice), which seems to kind of gut TPSH’s position.
Now, I’m a Hejda fan. So how can I overlook his Corsi? Well, out of the 186 defencemen who were on the ice for at least 500 draws, Hejda had the fifth toughest ratio of D/O zone draws. I put together a chart graphing D/O zone draw ratio against Corsi ratio:
The correlation of Corsi to D/O faceoff ratio for defencemen who were on the ice for at least 500 draws is -0.63. Of the 42 guys with a ratio of D/O faceoffs of 1.2 or better (Hejda was at 1.3), 3 of them had a positive Corsi. Nobody with a D/O faceoff ratio as high as Hejda’s posted a positive Corsi.
One of the axioms of the hockey staterati has been that context is everything. That applies to the new fangled stats too – you need to check the percentages and other factors for the guys at the extremes in order to get a real idea of why the results were what they were.