by PuckStopsHere on 09/15/12 at 02:12 PM ET
A few days ago I posted the team rankings by close score Fenwick compared with team Corsi. These are two schemes to try to rank team abilities at puck possession. The close score Fenwick system tracks missed shots and shots on goal when the game is within one goal in the first and second periods and tied in the third. The idea is this tracks puck possession when the game is close enough that no team has gone into a defensive shell or has given up defensive play in order to push for a tying goal. Team Corsi is slightly simpler. It tracks all attempted shots (this includes blocked shots which Fenwick doesn't) in all situations of 5 on 5 play.
Most teams have very similar rankings under both systems. A few do not. There are meaningful reasons for these differences that may show the superiority of one system over another. I looked at the case of the St Louis Blues who are first in close score Fenwick and ninth by team Corsi in 2011/12. The difference is that St Louis shuts things down when they have a lead more than other NHL teams and this keeps them from having good overall stats outside of close score situations.
Two more teams that show significant differences between the two systems are the New York teams. By close score Fenwick the New York Rangers are 14th and by team Corsi they are 25th. By close score Fenwick the New York Islanders are 18th and by team Corsi they are 26th.
Puck possession numbers show that both of these teams have a large discrepancy between both systems where close score Fenwick gives them a higher ranking. It also shows that there isn't much difference between these teams by puck possession ability despite the fact the New York Rangers were first in the East Conference and the New York Islanders were second to last in it. The most significant difference between these teams was goaltending - which is not significant in puck possession stats. The Rangers had Vezina winning Hart Trophy nominee Henrik Lundqvist and the Islanders had weaker goaltending. Evgeni Nabokov was solid but the rest of his backups were not.
The clear conclusion from these numbers is that the New York Rangers overachieved in 2011/12 and will not be able to keep it up. They may have overachieved very significantly if their team Corsi is the more meaningful number. The Islanders finished about where it would be expected by their team Corsi. They may be a better team than their finish showed - though not a playoff calibre team - if the close score Fenwick is more meaningful.
The main difference between these numbers for both teams comes from blocked shots. Corsi includes blocked shots and Fenwick does not. When measuring puck possession this distinction is meaningful. A blocked shot may be a positive defensive event and though some people fundamentally dislike "penalizing" a team for blocking a shot, it is not a good thing when measuring puck possession. If a team had to block a shot then their opponent must have possessed the puck.
Both New York teams are league leaders in blocking shots. This is a big part of their defensive scheme. They team to force their opponents into positions when they take shots that will be blocked. It is a tough defensive scheme to play because blocking shots leads to injuries and to weird deflections where the shot blocker is out of play. It can lead to screened goalies in cases of failed shot blocks. In some cases it can lead to a team doing well (as in the Rangers) or it can lead to continued failure (as in the Islanders). I think this difference is largely a function of goaltending and not the fact that the team blocks shots. Nevertheless, the tendency to force a team to take a shot that will be blocked creates more Corsi events against than might exist in a different defensive scheme. It does so largely by allowing opposing teams to possess the puck in positions where they will take blocked shots.
I think of the two numbers were are looking at, team Corsi is more meaningful because it includes blocked shots. It might be meaningful to look at close score Corsi situations instead of Fenwick ones because blocked shots would be included and thus puck possession would better be measured, but score effects are still taken into account. I think the tendency to look at close score Fenwick as a team puck possession stat is a mistake. Close score Corsi should be used instead. The blocked shots removed from the Fenwick system is meaningful and these New York teams show it.
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