Thursday, March 12, 2009

Hockey Blogosphere Dictionary: What the (Fugees) is a Corsi Number?

Corsi, not Corso, silly.

At the moment, Cycle like the Sedins is probably a "five out of ten" on the hockey newb-friendly scale we'd say. On one hand, there are niche-y references to hockey players and situations only a diehard can love. But we still put up pictures of bloody hockey players, make pun-y jokes and generally act too silly for our own good.

In an effort to make the hockey blogosphere a friendlier place, we'll occasionally try to explain some of the insider stuff to outsiders. (And help other insiders who don't know key phrases, events, etc.)

Don't have a clue about a term, phrase, crucial hockey event or what have you? Drop me an e-mail at

For the last two weeks, I've been seeing a stat that made me honest-to-God go blank: Corsi numbers. As a person once hateful toward mind numbing stat analysis, the concepts of deep contextual hockey stat breakdowns are still slowly absorbing into my gray matter.


Corsi Number : Frustrated with the minimal understanding of a player's impact shown by the plus/minus stat, statheads came up with another way to look at on-ice defense and offense.

The easiest one-line explanation of a player's Corsi Number is "the number of shots directed on net while a player is on the ice." That came from Hockey Numbers, which has a solid and more in-depth study of the Corsi Number:

"Corsi number is the number of shots directed towards the net while the player is on the ice. The number can be broken down into whose net the shots are directed towards (their own net (-) and their opponent's net (+)) similar to the plus minus statistic. The hope of course is that the Corsi plus minus would correlate well with the regular plus minus, but because the numbers will be 16x larger than plus minus numbers they'll be about 4x more accurate than the plus minus numbers."

So there it is for us, the drooling masses with our unwashed hair and stained T-shirts.


jamestobrien said...

Do you think this should be a running feature? Not sure off the top of my head what are some other terms that are unknown, but let me know.

Dominik said...

Yes, what is this "off-side" thing I always hear about?

No, I agree it would be a good series/feature, but for the life of me I can't think of something as useful yet as new/mysterious as Corsi. I remember I had to do some looking around to find it when I first heard of it.

Something perhaps as useful: A post telling people how to get a hold of the best stats like this, and where best to sort them. Also: a robot that fetches beer.

jamestobrien said...

Good calls all around, Dominik. I think that this could also be a good venue for "is (blank) a good stat or a nerd stat" debate, too.

p. said...

I believe there is already a stat for this. It's called "Shots". Not too many players make shots on their own net, and while the more common "Shots on goal" stat only reflects shots that had a chance of going directly into the net, I don't see how knowing the number of shots directed at one's own net would really define defensive responsibility more than the +/-.

RJ said...

To P.

"I don't see how knowing the number of shots directed at one's own net would really define defensive responsibility more than the +/-."

The reason that this is a more accurate representation of the popular +/- is that it is a larger sample size to draw the same conclusion. Because the Corsi stat is highly correlated (more often than not, the more shots you have the more likely it is you will score) with +/-, it gives a similar picture. Because the sample size of events (shots directed towards the net vs goals) there is less room for error, therefore making the stat more accurate. (General rule in statistics is that the larger the sampple size, the greater the accuracy of conclusions drawn from that sample).

Hope that makes the reasoning of the statistic more understandable.

jamestobrien said...

RJ explained it well. Corsi Numbers aren't everything, but they seem worth considering if nothing else.