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The Limits of Corsi

Every once in a while the Winnipeg Jets have a break and there is not a lot going on that is not us repeating ourselves. When this happens, I reach out to the masses to see what they want to read. This is one of those requests.

Vegas Golden Knights v Winnipeg Jets - Game Five Photo by Jason Halstead/Getty Images

One of the most predictive stats in hockey is Corsi or Fenwick, which helps show how frequently a team is directing the puck towards the opposition net. There is a correlation between this and how much a team has the puck. The logic is that the more you have the puck, the more likely you are to win because the other team cannot score when on defence.

However, there are limits to Corsi and Fenwick. Most of the limits work with another stat: PDO. PDO stands for nothing, but is the combined total of save percentage and shooting percentage. If it is calculated for a team it is the team PDO while individuals can also have both an individual PDO (there own shooting percentage and then the goalies save percentage when they are on the ice) or with on-ice PDO (the combined save-percentage and shooting percentage when the player is on the ice). Both of these numbers help tell a story.

Through a lot of testing, it was discovered that PDO of a good team that adds up to 100. Anything well above this mark and that team is riding the luck wave; way below and you are looking at a team that has bad luck. Luck is a key part of hockey and PDO is the catch-all stat that has been devised by those who first researched analytics in hockey to show it.

There are always teams that fall out of this bubble. A team like the Los Angeles Kings can have good possession numbers, but their system does not lend itself to offensive results based on their system. While we can explain low-possession teams scoring fairly easily, it is harder to do so for a good team. What PDO and Corsi allow someone to do is find a place where deeper research is needed. What are the Kings doing that makes it so hard for them to score? Is there something they can change to have better results or is the make-up of their team not conducive to scoring?

Corsi and Fenwick (mostly Corsi) are used by a lot of people to define if a team is “good” or not. While it is not a catch-all stat, it allows for a starting point to figuring out what is working or not working for a team. Corsi is a good starting point for a discussion about what teams are doing to find success or what is preventing them from finding success. Sometimes, that is all a stat needs to do. Hockey has a lot of moving parts and is harder to quantify than other sports. However, there are trends that can be found and then those trends can be followed to find what is actually plaguing teams.

Corsi is limited, but when combined with PDO, analysts can find what teams need to improve on and what they are doing well or uniquely so they can move forward. Teams can also do this as a starting point if they notice something is off in their results. Corsi is limited in some ways, but its uses are infinite.