Analytics (ice hockey)
In ice hockey, analytics is the analysis of the characteristics of hockey players and teams through the use of statistics and other tools to gain a greater understanding of the effects of their performance. Three commonly used statistics in ice hockey analytics are "Corsi" and "Fenwick", both of which use shot attempts to approximate puck possession, and "PDO", which is often considered a measure of luck.
Hockey Hall of Fame coach Roger Nielson is credited as being an early pioneer of analytics and used measures of his own invention as early as his tenure with the Peterborough Petes in the late 1960s. In modern usage, analytics have traditionally been the domain of hockey bloggers and amateur statisticians. They have been increasingly adopted by National Hockey League (NHL) organizations themselves, and reached mainstream usage when the NHL partnered with SAP SE to create an "enhanced" statistical package that coincided with the launch of a new website featuring analytical statistics during the 2014–15 season.
Corsi, called shot attempts (SAT) by the NHL, is the sum of shots on goal, missed shots and blocked shots. It is named after coach Jim Corsi, but was developed by an Edmonton Oilers blogger and fan who developed the statistic to better measure the workload of a goaltender during a game. Corsi is used to approximate puck possession – the length of time a player's team controls the puck – and is typically measured as either a ratio (like plus-minus) of shot attempts for less shot attempts against, or as a percentage. According to blogger Kent Wilson, most players will have a Corsi For percentage (CF%) between 40 and 60. A player or team ranked above 55% is often considered "elite".
Fenwick, called unblocked shot attempts (USAT) by the NHL, is a variant of Corsi that counts only shots on goal and missed shots; blocked shots are not included. It is named after blogger Matt Fenwick and is viewed as having a stronger correlation to scoring chances.
PDO, called SPSV% by the NHL, is the sum of a team's shooting percentage and its save percentage. PDO is usually measured at even strength, and based on the theory that most teams will ultimately regress toward a sum of 100, is often viewed as a proxy for how lucky a team is. According to Wilson, a player or team with a PDO over 102 is "probably not as good as they seem", while a player or team below 98 likely is better than they appear.
Zone starts is the ratio of how many face-offs a player is on for in the offensive zone relative to the defensive zone. A player who has a high zone start ratio will often have increased Corsi numbers due to starting in the offensive zone, while a player with a low zone start ratio will often have depressed Corsi numbers. Strategically, coaches may give their best offensive players more offensive zone starts to try and create extra scoring chances, while a team's best defensive players will typically have more defensive zone starts. In recent time, the use of zone starts in analysis has decreased. It has been determined that "on-the-fly" shifts account for more than half (58%) of all shifts.
Score effects and situational modifiers
While hockey's analytical statistics can be used to measure in any manpower situation, they are most often expressed relative to play at even strength. The statistics can also be viewed relative to "score effects". Corsi close and Corsi tied, for instance, are restricted to when one team leads by one goal or when the game is tied, respectively. The use of "close" stats is intended to reflect the fact that a team leading a game will tend to play more defensively, meaning the trailing team will often take more shot attempts.
Corsi close went under scrutiny that it did not predict future goals as well as unadjusted corsi, thus diminishing its value. Methods of weighting each shot by the score situation (score adjustment) has taken over as the method to adjust for score effects.
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