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"This shows how stupid the Corsi thing is..."

Following yesterday's article in the Globe & Mail, Don Cherry sputters (video here) uncontrollably about advanced statistics on Hockey Night in Canada.  After Ron McLean tells him that Ryan Johnson of the Vancouver Canucks has the worst Corsi number in the league:

"This shows how stupid the Corsi thing's a guy that every coach would want...this is how stupid guys come up with...trying to earn a living...they come up with dumb...they said this guy is the worst hockey player in the league...this guy is unbelievable and they call him the worst from that dumb thing that you did...and he's the worst player?  I'll tell you one thing...Vancouver loves this guy...he is unbelievable...and that dumb-dumb system you're talking about...I would love to have Ryan Johnson on my team and every coach would have him on too..."

Where to begin?  First, let's look at who the '+/-' statistic said was "the worst player in the league the last few years":


Year Player Team +/-
2009-10 Patrick O'Sullivan EDM -33
2008-09 Brendan Witt NYI -34
2007-08 Radek Bonk NSH -31
2006-07 Joffrey Lupul EDM -29
2005-06 Mark Recchi PIT -36


Oddly enough, these "worst" players averaged 18 minutes of ice time per game in these terrible seasons and all of them still had jobs the next season.  Sometimes legitimately bad players end up being last in the league in +/-, but usually it's just a good player playing a lot of minutes on a terrible team.  Context matters!  I won't belabor this point by listing the players who finished last in the league in goals, but suffice to say that there are a lot of players who get paid a lot of money even though they're the 'worst' in some category.

At any rate, one of the things I stress about Corsi is that it needs to be understood in context.  Yes, Ryan Johnson has the worst Corsi among regular players in the NHL - but at 5-on-5, he has also taken 67.9% of his faceoffs in Vancouver's defensive zone.  Johnson plays primarily on the 4th line and spends a lot of time dragging Darcy Hordichuk and Rick Rypien up-and-down the ice, so we'd expect his numbers to suffer for lack of better linemates.  That's why at -2, Johnson has one of the 'worst' plus/minuses on his team.

Johnson, of course, has other skills.  He's an above-average faceoff taker.  He blocks shots at a very high rate for a forward.  He plays on the second line penalty-kill.  And yet, he gets paid less than the NHL median salary.  He's behind Kyle Wellwood on the Canucks' depth chart at center.  The Canucks got a bargain when they signed him, but even if every coach would want him on their 4th line, NHL teams thought he wasn't worth much more than Mark Recchi or Colton Orr.  That's their judgment - not mine, not Corsi's.

One other issue that Don Cherry brings up is that shots that Ryan Johnson personally blocks are counted against him.  And why wouldn't they be?  When you block a shot, it means the other team had puck possession in your zone while you were on the ice.  That's not a positive thing.  Obviously when we evaluate Johnson as an individual, we would take his shot-blocking ability into account.  But if Darcy Hordichuk was on the ice with him and allowed the other team to control the puck - if we're trying to measure puck possession, we shouldn't give Hordichuk credit for Johnson's skill.

It's non-trivial to determine a player's value.  But Corsi does a good job of determining where the puck was when a player is on the ice.  It's heavily-driven by whether you start out with a defensive or offensive draw, and obviously it assigns group credit for individual skills.  But so do most other statistics that we don't sneer at - play with Mario Lemieux and you'll score a bunch of goals; it doesn't invalidate goal-scoring.  I have a feeling that if Don Cherry had coached an NHL team in the last 30 years, he might not be so dismissive of Jim Corsi.