Welcome to C of Stats, the inevitable result of a scientist and Flames fan who discovered advanced hockey stats. There's no better place to start this blog than with a miniature review of some of these "fancy" stats, focusing on what they are, why they're powerful, and how we can take them further. This serves as a concise introduction to the analytics community and sets the foundation for this blog's existence.
Our advanced stats saga begins with the Corsi and Fenwick stats, admittedly awkward names attributed to an NHL goalie coach who had nothing to do with the stat, and a blogger. Simply enough, Corsi and Fenwick count all the shots a team directs towards the opponent’s net: shots on goal, missed shots, and (for Corsi only) shots that are blocked. Both teams’ shot totals are then compared in what's called a shot differential. The premise is simple: the team that takes the most shots is the team that possesses the puck more. After all, puck possession is a prerequisite to shooting, and as it turns out, possession is critical to winning hockey games.
Corsi and Fenwick are solid metrics. They correlate strongly with winning hockey games and more importantly, they are better predictors of future goals and wins than measures using traditional stats. Note that the most salient feature of advanced stats is their predictiveness. Predictive hockey analytics are proven to repeatedly and reliably relate to goal scoring, which means we are actually permitted, by the laws of math and statistics, to use these numbers to judge and predict performance. And Corsi and Fenwick are better at this than any other metric to date (including, perhaps most of all, the opinion of many sports broadcasters). Like anything though, Corsi and Fenwick have limitations. Insofar as every shot directed towards the opponent's net is given equal weight, Corsi and Fenwick can only infer anything about possession, and offer no insight into the quality of shots teams generate. Surely shot quality is important, right?
The answer to this question is more complex and less conclusive than you might expect. There's no question shot quality exists – studies have shown it has a measurable and statistically significant impact on the game. However, these same studies reveal that shot quality pales in comparison to Corsi and Fenwick as a predictive variable for future goals and wins. "[Shot quality] is 4 to 5 times less important than shot differential," Tom Awad concluded back in 2010. It comes as a surprise to most – and leaves many observers including myself feeling uneasy – but shot quality as measured in this research does not offer much insight in to the game of hockey.
But how exactly is shot quality measured? In Awad’s analysis (and in the analyses conducted before him), five key factors are identified: the distance from which the shot is taken, whether the shot comes directly after a rebound, whether the shot comes directly after a turnover, the shot type (e.g. slapshot), and the manpower situation. These are all logical factors, but as mentioned they lack any substantial amount of predictability. So is that it for shot quality? Does the analytics community move on? Many are, and the research certainly seems to support this position. But could there be more to shot quality than the five factors identified? And if so, could additional factors be any more predictive? Recent (albeit preliminary) studies suggest this could very well be the case.
Since the start of the 2013-2014 season, Ryan Stimson has been tracking passes that lead to shot attempts, known as SAG (Shot Attempt Generation). His preliminary findings show that shots on goal taken as the direct result of a pass are about 50% more likely to result in goals than shots that are not the result of a pass. This makes intuitive sense because goalies and the defending players are out of position in the moments following a pass. Furthermore, Stimson discovered that the efficiency with which shooters can convert passes into shots on goal, known as SAGE, correlates with goal scoring to the tune of 88 to 99 percent. This is nearly a perfect correlation, which suggests that goals are reliably scored because of shots generated from passes. SAGE also correlates more strongly than any other metric - Corsi and Fenwick included - to wins. If you’ll pardon the pun, these are game-changing findings. Preliminary no doubt, but they suggest that passing is a critical factor of shot quality.
These promising findings require further analysis, and this is precisely the inspiration for C of Stats. This blog has joined Ryan Stimson's Passing Project, and is collecting passing data for all Calgary Flames games starting with the 2014-2015 season. Regardless of Stimson's findings, as hockey enthusiasts we can all agree that passing is an essential part of the game. It needs to be tracked. This data will be incredibly revelatory and provide new insights into the Flames, their opponents, and the game of hockey as a whole. I can't wait to share the data and resulting analyses with you.
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Whether you're new to advanced analytics, an expert statistician, or just a straight up hater, don't hesitate to contact me with questions, comments and the like. If you'd like to join the Passing Project, contact Ryan Stimson on Twitter @RK_Stimp or by email at hockeypassingstats@gmail.com
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References
McKenzie: The real story of how Corsi got its name. Bob McKenzie. http://www.tsn.ca/mckenzie-the-real-story-of-how-corsi-got-its-name-1.100011
What Statistics Are Meaningful In A Given Season? Steve Burtch. http://www.pensionplanpuppets.com/2013/7/10/4508094/what-statistics-are-meaningful-in-a-given-season-corsi-fenwick-PDO-hits-fights-blocked-shots
Numbers On Ice. Does Shot Quality Exist? Tom Awad. http://www.hockeyprospectus.com/puck/article.php?articleid=540
How passing relates to shooting percentage and close situations. Ryan Stimson. http://www.hockeyprospectus.com/stimson-how-passing-relates-to-shooting-percentage-and-close-situations/
The pass-tracking project: Passing and goals. Ryan Stimson. http://www.hockeyprospectus.com/the-pass-tracking-project-passing-and-goals/
2013-2014 Devils Passing Review: Efficiency and Winning. Ryan Stimson http://www.inlouwetrust.com/2014/7/28/5901789/efficiency-and-transition-offense
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