Nerd says what? A guide to how new Caps coach, GM use analytics


(Photo by Patrick Smith/Getty Images)

The Washington Capitals hired a bunch of nerds. Brian MacLellan, the new general manger, and Barry Trotz, the new coach, both appear to embrace advanced analytics and see potential in applying them to the hockey club.

“I think there is a strong correlation between Corsi, Fenwick and puck possession and I think you got to be aware of it,” MacLellan said during his introductory press conference yesterday. “And there are adjustments you can make to those numbers: offensive zone starts, defensive zone starts and other things.”

Nerd says what? Allow me translate.

Corsi and Fenwick are names used by geeks the analytic community as a proxy for puck possession during even strength. Corsi, named after former goaltender Jim Corsi, is simply the sum of a team or player’s even-strength shots on goal (including those missed or blocked) when he is on the ice. Fenwick, named after Matt Fenwick, is the same except it does not include blocked shots. It works just like the plus/minus statistic in hockey.

Both Corsi and Fenwick are counted as “For” or “Against”. “For” is a shot or event that happens while the player is on the ice that is on behalf of his team. “Against” is the same but for the opposing team. In general, Fenwick is usually regarded as a better indicator over a longer period of time.  Corsi is a better indicator over a shorter period of time.

For example, last season Alex Ovechkin was on the ice for 799 “Corsi events for” and 870 “against,” giving him (and his team) 47.9 percent of the shots when he was on the ice. For comparison, The Kings’ Anze Kopitar helped his team outshoot opponents 1,316 to 843 for 61 percent of the even-strength shot attempts. Taking a higher percentage of the shots while you are on the ice is obviously better and is more conducive to winning over the long haul.

At the team level, Chicago was the second best puck possession team after Los Angeles, seeing 55.5 percent of even-strength shot attempts (3,892 to 3,124) in their favor during the regular season while Toronto was the worst (3,259 to 4,342, 42.9 percent).

As for the adjustments MacLellan alluded to, how a player is deployed will affect his puck possession numbers.

For example, a player that plays on a good team, shares the ice with good linemates, and plays against weak competition is greatly advantaged over a player that plays on a poor team, shares the ice with poor linemates, and plays tough minutes.

Another factor that influences Corsi is starting zone location at even strength. That is, a player that starts his shifts more frequently in the offensive zone will, on average, have a better Corsi number than a player that starts his shifts more frequently in the defensive zone.

Two of the best examples of manipulating zone starts to best serve your players and organization can be found in Vancouver. The Sedin twins have taken 44 percent of their even-strength draws in the offensive zone for years and remain one of the highest ratios in the league.


2013-14 Vancouver Canucks player usage chart (Source: ExtraSkater.com)

Plus, Canucks general manager Mike Gillis cut Cody Hodgson’s defensive zone time by 77 percent prior to putting him on the trading block in an effort to inflate his value.

“That was by design,” admitted Gillis. “We put Cody on the ice in every offensive situation we could.”

We also need to adjust for score effects.

Score Effects takes over when a team has a lead greater than 1 goal, particularly late in the game.  Often the team with the sizeable lead will go into a defensive mode instead of continuing to press their offensive attack.  Football fans can think of this as being similar to a “prevent” defense.  This defensively minded style of play often allows the trailing team to make a push offensively.  This leads to more shots and thus higher possession and offensive zone time for the attacking (trailing) team.  Further, teams trailing as the game gets closer to its conclusion tend to throw caution to the wind in an effort to score, contributing further to the disparity in shot attempts.  In football, these would be likened to onside kicks, trick plays and Hail Mary passes.

Here is a recent example from Game 4 of the Western Conference finals. As you can see, the Kings took their foot off the gas after the score was 4-1 before the end of the second period.


Shot Attempt (Fenwick) Chart for CHI vs. LAK Game 4 (Source: Extraskater.com)

The Blackhawks outshot the Kings 24-21 by the end of the game, but the game was out of reach early.

MacLellan correctly cautions against using data like this blindly. “Data is as good as the analyst reading the data,” he said. But it is good to see the Capitals open to using all available tools to improve this club back to playoff contention.

Neil Greenberg analyzes advanced statistics for all sports and prefers to be called a geek rather than a nerd.
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