Sunday, November 08, 2009

More on Dubious NHL Shot Counting

Following up on the 'Shots On Net' post below, this is a chart showing the NHL's most dubious shot counters from the 08/09 season. Click to enlarge. Calgary and Edmonton are fringe qualifiers, but they are teams of interest around here, so I included them. All this information is for when the game is tied at even strength, to try and minize the noise.


By way of example, for Calgary:

On home ice the Flames NHL scorer recorded 50.5% of the Flames' shots-directed-at-net (Corsi) as shots on goal. And he recorded 58% for the opponent's shots/Corsi.

On the road, the aggregate totals of the NHL scorers in other rinks show the Flames with 53% shots/Corsi. And their opponents with a 61% shots/Corsi.

That's shown as a red line. The angle of the line indicates his home team bias. The nearer 45 degrees, the less that home team bias is indicated. So it looks like the person that the NHL employs to track shots-on-goal is a bit of a hard marker. But he's the same way for both teams playing on Saddledome ice. The shot bias is fairly significant. Some back of the envelope sums suggests a .004 or so hit on Kipper's save%.

The scorer at Rexall sees the game the same way as the Flames marker. The Toronto shot tracker is an extreme version of the same.

The Chicago scorer is the polar opposite, everything looks like a shot to this cat. But at least he seems fair to both teams.

The Buffalo and Tampa Bay counters show extreme home bias, they are flattering their goalies in a pretty significant way. I don't know how much .005 or .010 difference in save percentage matters come contract negotiation time, but it looks to me like befriending the shot tracker would be very worthwhile for an NHL goalie and his agent.

The Montreal guy/girl is tough when it comes to counting a Habs shot as being "on net", but he softens up when the other team's shoot the puck. I hope that the Canadiens goalies appreciate that.

Of course there is surely a lot of noise in here, teams like EDM and CGY may well just be coincidence, or at least the magnitude might be considerably less. The others though ... those are madass swings. Maybe somebody will look at past seasons and see if these tendencies persist.

Just generally, I think it is wiser to use shots% or shot ratio, instead of shots+/-, when looking at teams like CGY, EDM and CHI.

2 Comments:

Blogger JLikens said...

I love looking at this stuff.

The data points for all 'away' scorers are relatively clustered, as they should be, save for those of the Flames and Blackhawks. This suggests that those teams really are less likely to get shots through than the opposition.

I assume that the Lightning changed scorers after the 07-08 season, based on the fact that their team save percentage was absolutely terrible from 05-08. If there was no change, that means that their goalies were putting up 80's-esque save percentage numbers in spite of getting the benefit of the doubt from the shot recorder. That's a scary prospect to consider.

11/09/2009 12:20 pm  
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