Corsi is an advanced statistic used in the National Hockey League to measure shot attempt differential while at even strength play. This includes shots on goal, missed shots on goal, and blocked shot attempts towards the opposition’s net minus the same shot attempts directed at your own team’s net.
The Corsi number was named by Tim Barnes, a financial analyst from Chicago working under the pseudonym Vic Ferrari. He had heard former Buffalo Sabres general manager Darcy Regier talking about shot differential on the radio, and then proceeded to develop a formula to accurately display shot differential. Ferrari originally wanted to name it the Regier number, but he didn’t think it sounded right. He then considered calling it the Ruff number after former Buffalo Sabres head coach Lindy Ruff but he didn’t think that was appropriate either. Ferrari ended up searching Buffalo Sabres staff, found a picture of Jim Corsi, and chose his name because he liked Corsi's mustache.
- Corsi = Shot attempts FOR – Shot Attempts AGAINST
- Corsi ON measures an individual’s shot attempt differential while he is on the ice. This is calculated as:
- Corsi ON = (Total Corsi) x (60 mins)/(player’s total ice time on the power play)
- Corsi REL = Corsi ON – Corsi OFF. This measures a player’s Corsi number when he specifically is on the ice minus his Corsi number when he is off the ice.
Because shot attempts are often taken in the offensive zone, Corsi numbers provide an indication of the time a team spends in the offensive zone, versus time spent in their defensive zone. Positive Corsi numbers tells you that the team spends more time in the offensive zone than the defensive zone, while negative Corsi numbers tells you the team spends more time in the defensive zone than offensive zone. Possession is a good stat to take into account because the team with the higher possession numbers at the end of the game generally wins. Corsi can be broken down into four categories: Corsi Ahead, Corsi Even, Corsi Close, and Corsi behind. In order, the categories refer to what a team or player’s Corsi number is when they are ahead in the game, when the game is tied, when the score of the game only differs by one goal no matter who is ahead, and when the score is behind, in that order. Each of these stats will tell a coach whom he should be putting out on the ice depending on the score of the game.
While Corsi may provide a more accurate evaluation of players' contributions to a winning effort than plus-minus (giving a plus to players who are on the ice when a goal is scored and a minus to players who are on the ice when a goal is scored on their own net), it does have its own criticisms. For example, a player is on the ice for 30 shots on net and 20 shots against. This player is a defensive defenseman, and in this situation he only helped create 5 shots on net but his mistakes led to 15 shots against. This tells us his real impact on the game is -10 Corsi, but on the game sheet at the end of the game his Corsi number will be +10. This is because he was playing with better players around him and that boosted his Corsi number. Essentially, a good player playing consistently with bad players will have a lower Corsi number, while a good player playing with great players will get a boost. For this reason, additional advanced metrics, for instance using raw Corsi values adjusted against frequent on-ice teammates', can provide a more accurate assessment of individual players' contributions.
- McKenzie, Bob. "McKenzie: The real story of how Corsi got its name". www.tsn.ca. Bell Media. Retrieved 2 February 2015.
- Staples, David. "Why Corsi numbers are an unreliable base stat for rating players". blogs.edmontonjournal.com. Edmonton Journal. Retrieved 3 February 2015.