Advanced Analytics in the NHL: Corsi

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Credit: goldjournal.com

There has been much controversy over the past few seasons regarding advanced statistics. Some people believe it isn’t an indication of how good a player really is. Others think plus/minus is still a legitimate stat to be used. Corsi is one of the basic stats to use when looking at a players’ possession. I will take a brief look at it in this article and demonstrate how to calculate and apply it.

I used to be a fan of plus/minus. It gave me a simple, clear understanding of a players’ defensive abilities and if said player was good in his own end. I knew that players with a low plus/minus were often depicted as a defensive liability.

But as I grew up and started watching more hockey, I started to understand how useless plus/minus really is. It doesn’t give a clear indication of what people need to know when it comes to a players’ defensive play and his possession. This is where advanced stats come into play.

What is Corsi?

Corsi measures a players puck possession by using his shot attempts. Even if the shot is on net, blocked, misses the net or is in the back of the net, it is registered as a shot attempt.

Here is an example. If I take Flyers rookie Travis Konecny and want to know his Corsi in all situations, I would add his Corsi For (CF) and divide it by the total of his Corsi For and Corsi Against (CA). It would amount to CF / CF + CA = CF%.

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Source: hockey-reference.com

To find out Konecny’s CF%, I would do: 197 / 197+165 = 54.4%

But what does this number mean?

When a player has a CF% above 50%, it usually means the team was controlling the play a little more and getting more offensive zone time. Most of the NHL ranges between 40% and 60%. If a player is at 60% +, it usually means his team spent most of their time in the offensive zone generating chances. If a player is at 40% or less, it means his team was getting dominated by the opposition.

Relative Corsi For % at Even-Strength

As for CF% rel (Relative Corsi For % at Even Strength), it compares the players’ even strength Corsi relative to the even strength Corsi of his team when said player is not on the ice. So, using Konecny again, the equation would be:

CF% with Konecny on the ice – CF% with Konecny off the ice* = CF% rel

*To find out the Flyers CF% with Konecny off the ice, simply take his CF% (54.4) and subtract his CF% rel (0.7). 

54.4 – 0.7 = 53.7

So, 54.4% – 53.7% = 0.7 CF% rel. 

Once again, what does this number mean?

The 0.7 is the difference between the team’s CF% when Konecny is on the ice vs when he isn’t on the ice, therefore, 0.7% better.

Obviously, this is only a small sample size, but the concept remains the same.

It may seem a little complicated, but once you find out the meaning behind the numbers, Corsi becomes very concrete and simple. This is why it’s so effective and measures a player much better than plus/minus.

Brandon Murphy – @2murphy8

 

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