Eventually, “Corsi” is going to have to take on a different name. “Corsi” had a good run, but in the end, it’s difficult to carve widespread acceptance of statistical concepts named for the person that created it. Often, I’ll see somebody write out CORSI as if it were an acronym for something.
“Corsi” isn’t really particularly complicated. It’s the number of shot attempts for, minus the number of shot attempts against. It can be used for both a team or an individual. For the team, “Corsi” would count up all the shot attempts a team took in even strength situations and subtract them by the ones their opponent fired against their net. For an individual, you just look at the time he was on the ice.
It’s not a real difficult concept, nor is it difficult to understand what it means. “Corsi” doesn’t assume that every single shot taken on goal is of equal value. All “Corsi” does is approximate zone time. If Pittsburgh takes 5 shots at the New York Islanders’ net and the Islanders take 1 shot at the Penguins net, the logical assumption is that the puck spent more time in Pittsburgh’s offensive end. It doesn’t mean anything more than that. Heck, the one Islander shot could be a breakaway from Michael Grabner or Frans Nielsen. It doesn’t change that the majority of the game was spent with the puck on the stick of a Penguin player.
There’s no substitute for real good puck possession.. In the first half of 2011, the Minnesota Wild drew glowing reviews for their ability to win games despite being outshot. Like the 2013 Toronto Maple Leafs, a lot of proponents of defensive coaching systems are suggesting that Randy Carlyle is creating a style of play that makes the shots given up by Toronto easy on the goalies.
A few guys have transitioned from counting scoring chances to zone entries. I still count scoring chances for Toronto Leafs games because I think it’s a good gateway micro statistic. Everybody knows what a scoring chance is, and over a long stretch of games, it’s found that scoring chance differentials sync up nicely with Corsi, the puck-possession indicator.
Basically, when you spend a lot of time with the puck in your end, you’re liable to give up a lot of scoring chances. There is no magical formula or special powder at the NHL level that will help Randy Carlyle coach Mark Fraser to give up more shots between scoring chances than he should. Maybe you can a small bit, but knowing the predictive power of simple shot differential and possession numerals, it’s largely inconsequential over a span of games. There’s no substitute for good possession.
When I say that scoring chances are a gateway statistic, it’s because it bridges the gap between “goals” and “Corsi”, as in you’re giving yourself a wider range of things to analyze than +/- numbers to determine player effectiveness, but aren’t alienating a learning base.
A scoring chance is defined as a clear play directed toward the opposing net from a dangerous scoring area – loosely defined as the top of the circle in and inside the faceoff dots (nicknamed the Home Plate), though sometimes slightly more generous than that depending on the amount of immediately-preceding puck movement or screens in front of the net. Blocked shots are generally not included but missed shots are. A player is awarded a scoring chance anytime he is on the ice and someone from either team has a chance to score. He is awarded a “chance for” if someone on his team has a chance to score and a “chance against” if the opposing team has a chance to score.
The definition isn’t super objective and still lends some room for interpretation. Some folks are more generous on certain shots than others, meaning that for individual games, one team may land an extra scoring chance or two, but in the long run, the differences are caught on either end. Rather than counting a team 100-100, a more generous counter may have it 112-111 or a less generous one could have it 88-89. Either way, those differences won’t change too much in the way we analyze things, since they’re small events taking place in context of a large season.
I’ll bring up the Toronto and Pittsburgh game, a game I was counting chances. The Penguins were excellent. They made Phil Kessel look like an AHLer and the only Leafs worth their salt were the best defensive ones they have on that team: Mikhail Grabovski and Dion Phaneuf who did a job to sort of shut down Sidney Crosby. Evgeni Malkin was a horse that somehow went unheralded.
Pittsburgh had 17 scoring chances against Toronto, and Toronto had just 6 against Pittsburgh. By rights, it shouldn’t have been a very close game. But these are the Toronto Maple Leafs, who have a very good goaltender, and these are the Pittsburgh Penguins, who don’t really have a good goaltender. Here’s the demeanour of the very good goaltender after the game, per Jonas Siegel of TSN:
Hunched back in his dressing room stall James Reimer appeared as you would rarely see him. Shoulders slumped. Arms folded. A piercing stare of anger gripping his face.
“Just feeling like you let down the team,” he told TSN.ca on Saturday evening, following a 5-4 shootout loss to the Penguins at the Air Canada Centre, a defeat which snapped a personal six-game win streak.
“There’s games where you don’t play well,” he continued, his emotions raw after the loss, “and sometimes you don’t get a chance to be the difference and it’s frustrating and it sucks, but you move on and you be better the next day. And tonight’s double because you had a chance to redeem yourself and you didn’t. It’s like a double letdown I guess you could say.”
According to Corsi, Toronto got out-possessed at even strength 63-50. Calculating that as a percentage, that’s just 44.2% ( 50 / 113 ) of the shots that went Toronto’s way, and just 17.6% of the scoring chances. Despite this, Reimer looked battered and beaten, convinced that because of one bad goal he allowed in regulation, plus whiffing on two shootout attempts, that he had cost his team the game.
Hockey, as I discussed Friday, is a results-driven business, where managers that try to gain an edge simply don’t have the time to let their theories play out over a sample large enough to deem them worthy. People like immediacy, and by praising Toronto’s defensive efforts this season, it gives off the illusion that Randy Carlyle has built a stable foundation in Toronto that’s sustainable. It isn’t really, unless Reimer can continue to put up the numbers he has over his tenure in Toronto.
Since Reimer got called up to the Leafs, actually, his save percentage at even strength is .925, a few points above the NHL average over that span. The other goaltenders Toronto deployed, who faced the same porous defence and the same shots from the same angles, registered a .909 at even strength, which is below the level you could expect from a call-up at that position. (Stats from this and this, and NHL.com’s special teams page for goalies)
Had Reimer been healthy all of last year, the jobs of former coach Ron Wilson and former general manager Brian Burke would have been saved. Reimer has been able to make a bad defence look not only competent, but to the point where the team can be massively out-played, make it to overtime and still make it look like Reimer was at fault. Ben Scrivens this year has had a similar effect on our perception of the Leafs as a defensive unit, but they’ve been bleeding scoring chances of late, now that opponents are starting to take advantage of the territorial, or “Corsi”, advantage that comes with playing against the Toronto Maple Leafs.
The focus on immediate results, though, skew what’s really going on. It takes a great goaltender: Pekka Rinne in Nashville or Henrik Lundqvist in New York are good examples, to continually elevate a team beyond its puck possession record. Over the short term, though, a goaltender like Reimer, or Victor Fasth or Corey Crawford, can warp our perception of a team’s full potential and make them look a heck of a lot better than they really are.