Sunday, August 03, 2008

Measuring Quality Of Opposition

One sabermetrics and hockey problem that can be addressed using the on/off ice adjustment +/- is the strength of opposition that players face. This helps to correct one of the weaknesses in +/- ratings. Players do not play the same role for their team. Some play against tougher opposition (ie. first line players) while others tend to play against weaker opposition (third and fourth liners). Credit for doing this goes to Gabriel Desjardins of behind the net.

This can be measured by calculating the time average on/off ice adjusted +/- rating of the players who play against a given player. A player who plays against top players in +/- has a hard time then one who plays against the bottom ones. The adjusted +/- of all five players on the ice in opposition to a player is averaged between the five players and in time and then compared to the time average for their team's opponents (which is usually near - but not exactly - equal to zero). We can see from this which players play the hard minutes and which ones play the easier ones. A player who consistently plays against hard opposition is a better player than his +/- shows and one who is protected from hard minutes is not as good. The problem with this calculation is that is uses on/off ice adjusted +/- with its inherent flaws as a starting point, so any of those flaws will carry through the calculation.

Here are the ten players who played against the toughest opposition in 2007/08 (limited to players who played in 050 games or more):

Top 10 Quality of Opposition Ratings 2007/08
RankPlayerTeamQ of Opp Adjusted +/-
1Sami PahlssonAna0.18-1.23
2Rob NiedermayerAna0.17-0.94
3Keith BallardPhx0.16+0.66
4Nicklas LidstromDet0.16+1.66
5Derek MorrisPhx0.16+1.01
6Travis MoenAna0.16-1.08
7Jan HejdaCBJ0.16+1.40
8Jay PandolfoNJ0.16+0.85
9Mikko KoivuMin0.15+1.28
10Adam FooteCol0.15-0.03

This is a list of some of the best checkers in the NHL. These are players who are consistently used against the top scorers in the NHL. Two odd observations jump out when looking at this list. Only Jay Pandolfo plays on an East Conference team. Why is this? Does having a number of games against the weaker Southeast Conference make it hard to have a high quality of opposition for an East Conference team? Also, the only significantly negative players in their adjusted +/- are the Anaheim checking line of Sami Pahlsson, Rob Niedermayer and Travis Moen. Is this meaningful? It appears to show that this line struggled more in their hard minutes than any other players on this list.

Anaheim checkers Sami Pahlsson and Rob Niedermayer played the hardest minutes. They are followed by Keith Ballard of Phoenix (now traded to Florida). Nicklas Lidstrom is next. Lidstrom had an exceptionally good +/- given how hard his opposition was. Next up come linemates of the earlier players on the list in Derek Morris of Phoenix and Travis Moen of Anaheim. Jan Hejda follows as a successful checking defenceman in Columbus. Jay Pandolfo is next as the only east player on the list. Mikko Koivu of Minnesota and Adam Foote, who split his season between Columbus and Colorado finish out the list.

Here are the ten players who played against the weakest opposition last season:

Worst 10 Quality of Opposition Ratings 2007/08
RankPlayerTeamQ of Opp Adjusted +/-
1Aaron DowneyDet-0.22-1.26
2Riley CotePhi-0.21+0.73
3Ole-Kristian TollefsenCBJ-0.19-0.13
4Dwayne KingStL-0.19-0.91
5George ParrosAna-0.18+0.17
6Kris RussellCBJ-0.18-0.96
7Eric GodardCal-0.17-2.15
8Nolan PrattBuf-0.16-0.78
9Nathan PaetschBuf-0.16+0.32
10Shawn ThorntonBos-0.16-0.03

This is a list of players who were shown very little faith from their coaching staff. They rarely played against good opposition and were often reserved for situations where they played against easy opposition. Those who played against low quality of opposition and still put up poor adjusted +/- ratings (such as Eric Godard and Aaron Downey) probably should no longer be in the NHL.

Aaron Downey leads up this list. He offered little to his Red Wings team last season. He is followed by Riley Cote, who was used only as a goon by the Flyers. Ole-Kristian Tollefsen is next. He was heavily protected on the Columbus defence. Next up is Dwayne (D.J.) King who offered little to the St Louis Blues. George Parros was the Anaheim Duck goon. Kris Russell was heavily protected in his rookie season on the Columbus defence. Eric Godard was a goon in Calgary. Nolan Pratt and Nathan Paetsch played against easy opposition in Buffalo. Finally, Shawn Thornton played against limited opposition in Boston. None of these players were key to their team. All were reserved for situations where they could play against low quality of opposition.

Quality of opposition can be measured using the on/off ice adjusted +/- framework. It carries with it the flaws inherent in the system but does a good job of identifying players who play against high and low quality opposition. Those who play against high quality opposition should be ranked better than their +/- (or other stats) show. This is primarily a list of the best checkers in the NHL. Those who played against poor competition are borderline NHL players at best and those who failed in that situation should be out of the NHL soon.

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