The first thing
Jim Corsi wants the world to know? He didn’t invent the Corsi stat.
If that is a mystery to you, maybe you don’t know who Corsi is or what the stat named after him represents. If so, you haven’t been paying attention to the statistics revolution in the NHL that has made the last two months hockey’s summer of analytics.
Throughout the NHL, teams like
the Maple Leafs, Devils, Penguins and Oilers have been gobbling up executives and statisticians who can walk them through what the blogosphere has been promoting for years — what some call analytics, or advanced statistics.
It’s growing social-media-powered movement with a fanatical following that believes there are means to measure a hockey player’s contribution to a team beyond the obvious stats of goals, assists and ice time.
And it all started with Corsi, hired this summer as goalie coach of the St. Louis Blues; he was previously with the Buffalo Sabres. He might otherwise be known as the WHA goalie who got a cup of coffee in the NHL with the Edmonton Oilers and, though born in Montreal, played on Italy’s national team.
But the stat named after him is his legacy.
“I’m humbled and happy because it gives coaches and fans and some reporters a way to try to address what a player’s contribution is to a game,” said Corsi, in an interview with
thestar.com.
An outside-the-box thinker, Corsi was trying to measure just how busy his goalies were in a game. He didn’t believe the simple shots-against total — usually around 30 a game — was totally reflective of just how busy a goalie was. And since it’s up to the goalie coach to ensure the goalie is in shape, it was up to Corsi to find out how much workout time goalies needed between games.
So he added all shots and shot attempts, including ones that went wide, and ones that were blocked, figuring a goalie had to be in position or moving around regardless. He reasoned the shot total was more in the region of 50 to 70.
There are more shots and shot attempts in a game than goals, meaning the larger sample size of Corsi events is more reflective of a player’s performance than whether a player is on the ice for an unlucky bounce.
By measuring the various shots in 5-on-5 situations — like plus-minus — it puts all players on a level playing field. The stars don’t get the advantage that power plays give them. The grinders aren’t hurt by their time killing penalties. They can be measured with various linemates and against strong or weak opposition.
At the same time, the blogosphere was trying to find out what teams were best at puck possession. The NHL dropped time of possession as a stat in 2002. So bloggers turned to Corsi as its proxy, figuring if one team shot the puck more than the other team, it meant one team controlled the puck more than the other team.
The blogosphere realized that teams with good Corsi numbers typically went very deep in the playoffs. They told anyone who would listen — and, in the beginning, few did — that a good Corsi rating was a predictor of what was to come.