Thursday, May 07, 2009

Scoring Chances: Part VI of Many. The Problem with the PK


Shots metrics like corsi don't work worth a damn on special teams. But now we have scoring chances.

Dennis was sure that the problem with the PK was the skaters. I thought that Roloson was just letting in too many, or shooters were making their shots, luck and all that. It appears that Dennis was completely right.

The goals per scoring chance during even strength hockey was .22.
The goals per scoring chance during the PK was .22.

So like many other checks on Dennis' results, a few of which I listed in Part I, it's eerily consistent.

Roloson's PPsave% was terrible this year, but it looks like it's not his fault at all. The Oilers not only gave up too many shots, as we all knew, but that they gave up a disporportionate amount of scoring chances per shot. And that's on the coaching staff and the skaters, no way around it.

Contrarian goalie is currently revising a post seeing how EVsave% changed from season to season for goalies that changed teams. It's a clever idea. If he accounts for sample size (for both before and after seasons) I suspect he'll find that there is next to nothing in it, but we'll see. BUT, I think that if the same test is applied to PPsave%, we'll see some dramatic shifts.

3 Comments:

Blogger sunnymehta.com said...

damn vic you're on fire. great stuff lately.

care to speculate on why you think skaters other than goalies are better able to control save percentage on the PK compared to ES?

it seems to me (correct me if i'm wrong here) that part of your premise at ES is that it's the offensive players who are in control of which shots they take (as opposed to it being dictated/guided by defenses). if that's true, wouldn't it be more true on a PK, that defenses would basically be completely at the mercy of good offensive PP units?

5/07/2009 7:17 pm  
Blogger Vic Ferrari said...

I don't know. I know that this has been the case for years, the spread of PK save%s for the population is too wide for random chance to explain.

Now it's not mammoth or anything, probably far less than most hockey fans think exists already. But it's there. And far less than the effect of pitchers on BABIP I expect (absolutely less than the effect of hitters on BABIP) to use the baseball comparable you brought up earlier.

Frankly, I don't notice it when I watch the games. Maybe first unit PPs are the ones that are getting the shots? I dunno. I mean you'd expect the goals per chance to be a bit higher on PPs too, just because usually you've got more PP players with good finish on the ice. Not the case with the Oilers this year though, unless maybe the Oilers got a touch lucky (yikes! Doesn't bear thinking about).

I'm at a loss to explain the phenomenon.

There also seems to be a measurable effect of defender on shot quality. Not enough to say "player X prevents scorng chances at a better rate" definitvely. But it's there in the general population. Go figure.

5/07/2009 8:50 pm  
Blogger Vic Ferrari said...

Oops, looks like the scoring chances don't include the 5v3 chances for up to xmas but not after.

So this is all a bit of a mess. My bad.

Special teams remain highly unpredictable, to me at least.

5/08/2009 11:56 am  

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