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Stats: What is the Corsi Rating?

Over the past few years, different statistics in hockey have been given increased focus as teams try to gain any insight and advantage they can. Several of these statistics you may have heard of before – names like Corsi and Fenwick, are being heard more and more frequently in the hockey community. The rise of several websites that track these statistics makes it easier for fans to access this information, but just how useful are these new metrics, can we use them to make any predictions?

In the coming weeks I’ll be looking a little closer at some of these different statistics and what they can be used for. This week we’ll take a look at the 5-on-5 Corsi % of teams in the regular season to see if it can predict success in the playoffs.

The Corsi Rating was named after Jim Corsi, the Buffalo Sabres goaltending coach at the time of it’s creation, who was looking for alternatives to tracking shot attempts. If this is the first you’ve heard of the Corsi Rating, it’s actually much simpler to calculate than you may expect. A team’s Corsi Rating for a game is just the difference between the number of shots they put towards their opponents net and the number of shots their opponent puts towards their net. In the calculation, the total shots number includes all shots on net, wide, or blocked.

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A team that puts more pucks towards their opponents net will have a positive Corsi Rating, and if the opposite is true they will have a negative rating. A team’s Corsi % is just the ratio of a team’s total shots to the game’s total shot attempts, again including all attempts that are blocked or wide.

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If two teams direct equal shots towards their opponents goals, both will have a Corsi % of 50%. The theory behind the rating is that good teams will spend more time possessing the puck and as a result will take more shots than they allow, leading to a better Corsi Rating. Accurate Corsi numbers go back 9 years to the 2004-05 lockout, as before 2005 the league didn’t track wide or blocked shots. All statistics used in this article are based on those 9 years of data.

Since the 2004-05 lockout, of the 16 teams who made the playoffs each year (144 total), 29 teams were not ranked in the top-20 by Corsi % (about 3.2 each year), so having a good Corsi Rating seems to help in making the playoffs. Can a team’s Corsi Rating tell us about how well they will do further into the playoffs?

 

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The x-axis of this graph represents the top group of teams. As an example, teams ranked in the top 8 by Corsi % made the playoffs about 82% of the time, advanced past the 1st round about 44% of the time, past the 2nd round 25% of the time, and advanced to the Stanley Cup Final about 15% of the time. The curves for making the playoffs and advancing through the 1st round are reasonably straight lines, suggesting the Corsi Rating doesn’t have much of an effect here. The curves representing advancing through the 2nd and 3rd rounds have much steeper slopes towards the higher ranked teams, so the Corsi rating may be able to provide some insight into the later rounds of the playoffs.

One problem is determining how much effect this actually has on a league’s performance in the playoffs. Making it beyond the first round 50% of the time as a top-6 ranked Corsi % team seems like a decent success rate, but how is it in comparison to any other way we could try to predict success? The most common way of predicting a team’s post-season outcome is to reflect on their regular season point total and resulting position in the standings. How does the Corsi % compare to plain points? Obviously a team’s regular season point production has a direct correlation to whether or not they make the playoffs, but what about advancing through further rounds?

 

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We would expect ideally to see 50% of the teams ranked in the top 16 to make it past the 1st round, but because the different conferences allow for  teams to make the playoffs that may be ranked lower than 16th league-wide there is a slight variance. As noted above, Corsi % doesn’t seem to be the greatest predictor of a team moving past the 1st round, usually their position in the standings is better. What’s interesting is there seems to be a pretty significant weight associated with finishing as the top seed in points that makes it harder to advance through the first round – 4 of the last 9 President’s Trophy winners have been bounced in their opening series, even though all of those teams were ranked in the top 7 in Corsi %.

 

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The trend with teams finishing with more regular season points advancing further in the playoffs still exists to some degree here, but the Corsi Ranking is starting to prove somewhat relevant as some of the top ranked teams are having consistent success in the 2nd round. On average, 1 of the final 4 teams in the playoffs each year has been either 1st or 2nd by Corsi %.

 

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Predicting the final 2 teams is difficult and to survive this far often comes down to intangibles like lucky bounces and some players sheer will to win. Looking at the above graph, you can see it is hard to determine accurately who will make it to the Stanley Cup Final based on the metrics we’ve been using, but Corsi % is now as good of a predictor as points in the lower ranks and even better in the higher ranked teams. The top-ranked team in Corsi % has made the Stanley Cup Finals in 4 of the last 9 years, and has gone on to win the Stanley Cup in 3 of those years. On average the Finals consist of one team ranked top-5 in Corsi %, with 2006 being the only year the Stanley Cup Finals were without one.

 

 

For a different perspective, I reseeded the teams making the playoffs each year based on their Corsi %. If the Corsi % had no relevance to playoff success these lines would be horizontal since each team would have an equal chance of going deeper into the playoffs, no matter their Corsi %. There doesn’t seem to be much effect on the lower ranked teams, but the top-3 or -4 have a clear advantage over the rest. This agrees well with the fact that 3 of the top-rated Corsi % teams have gone on to win the cup since 2006. In fact, 3 of the 6 remaining Stanley Cups handed out over the past 9 years were won by teams ranked 2,3, or 4 by Corsi %.

Making predictions with the Corsi % will prove to be challenging for most of the league, but it will be interesting to see how the top few teams based on regular season Corsi % finish the playoffs this year. We’re about 1/3 of the way through the regular season, with the top 5 Corsi % teams in order currently being Chicago, Minnesota, Tampa Bay, Detroit, and Nashville. If this was the end of the season, chances are we’d see at least one of those teams in the Stanley Cup Finals, with Chicago having a 1/3 chance to win the Cup.


 

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All Corsi statistics taken from war-on-ice.com

Comments

  1. AvatarRicharddip

    Shot attempts and unblocked shot attempts can be expressed at a rate per 60 minutes of ice time. This helps even the playing field when it comes to analyzing players who receive different amounts of ice time.

    Reply

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