by PuckStopsHere on 06/19/12 at 01:23 PM ET
A couple days ago I posted the top 20 players by their unadjusted Corsi ratings in 2011/12. Generally it was a talented well respected group of players, but a few people on the list raise some eyebrows. One player who seems overrated by his Corsi rating is Justin Williams of the Los Angeles Kings. He is the fourth highest in the league in the 2011/12 season with a +404 rating. This makes him the highest non-Boston Bruin on the list. He is not new to top Corsi lists. In 2010/11 he was the 17th highest in the league. He is consistently a very good player when ranked by puck possession stats such as Corsi. His ranking is higher than one might expect as there is no reasonable argument that Williams is among the 20 best players in the NHL.
Williams is overrated by Corsi for several predictable reasons. First he plays on a good team. The Los Angeles Kings were one of the better teams in the league according to their puck possession numbers. They may have been the eighth seed but they were significantly better than a traditional eighth seed and showed this by winning the Stanley Cup. A key player on a good puck possession team will post a good Corsi. Williams also benefits by playing with good linemates. Anze Kopitar is usually on his forward line and Kopitar is a very good two-way player. He is among the best puck possession players in the league (he ranks right below Williams this season).
That leads to the question of how Williams can have a higher Corsi than his linemate Kopitar. The difference between them is not significant. It is only nine points. That difference is small enough to be random error in a Corsi measurement. Unlike Kopitar, Williams is not a solid two-way player. He rarely plays in defensive situations such as the penalty kill. His role is largely offensive. This allows Williams the benefit of playing with Kopitar in the more offensive shifts when it is easier to improve your Corsi rating and he is not on the ice in the more defensive shifts where a player might have a negative Corsi. Kopitar however plays these shifts. Thus Williams benefits from good linemates and a more offensive role. This allows him to post a higher Corsi rating than he might have in another role.
Corsi ratings are context dependent. This gives them great value as a lot of information can be drawn from them. It is also can make them hard to understand because their analysis is never simple. The easiest conclusion from Justin Williams’s Corsi is that he played very well in the role he was given. Another clear conclusion is that this role is suited toward him and he would not likely do so well in another role. This role is not as difficult as the role that most other players play. The problem of isolating the value of a player from his role is a difficult one. Williams is an example of a player who is overrated by his Corsi rating if we look at raw numbers.
Justin Williams is a good player who is a solid member of the Los Angeles Kings core. He plays a role that is well suited to him. He consistently posts a very good Corsi rating. This is as much a sign that he is well suited to his offensive role as his being a top player. There are other examples of players like this. Chris Kunitz of Pittsburgh and Alexandre Burrows of Vancouver usually post very good Corsi ratings (both are top players this year) and both are as much products of their role with their team as they are top players. Isolating a player’s value from the context of his role with his team is a difficult problem. There is no one clear method to do this. Developing a reliable method to do this would be a great benefit to Corsi analysis, which is already a valuable method to understand hockey.
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