Over the past couple of weeks I have had several comment discussions regarding some of my recent posts on player evaluation and Norris and Hart trophy candidates which centered around which is a better method for evaluating players: corsi vs goal based evaluation. A lot of people, maybe the majority of those within the advanced hockey stat community, seem to prefer corsi based analysis while I prefer goal based analysis and I hope to explain why with this post. I have explained much of this previously but hopefully this post will put it all into one simple easy to understand package.
There are two main objectives for a player when the coach puts him on the ice: 1. Help his team score a goal. 2. Help his team stop the opposing team from scoring a goal. Depending on the situation and the player the coach may prioritize one of those over the other. For example, a defensive player may be tasked primarily with shutting down an opposing teams offensive players and scoring a goal is really a very minor objective. Late in a game when a team is down a goal the opposite is true and the primary objective, if not sole objective, is to score a goal.
I think we can all agree on the previous paragraph. Goals are what matter in hockey so right there we have the #1 reason why goals should be used in player evaluation. The problem is, goals are a relatively rare event and thus ‘luck’ can have a serious impact on our player analysis results due to the small sample size that goals provide. This brought on the concept of corsi which is nothing more than shot attempts and is used as a proxy for scoring chances. The benefit of corsi is that shot attempts occur about 10 times often as goals which gives us a larger sample size to evaluate players.