DIGR: A Defense Independent Rating of NHL Goaltenders using Spatially Smoothed Save Percentage Maps

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Michael E. Schuckers


Abstract: Evaluation of NHL goalies is often done by comparing their save percentage. These save percentages depend highly upon the defense in front of each goalie and the difficulty of shots that each goalie faces. In this paper we introduce a new methodology for evaluating NHL goalies that does not depend upon the distribution of shots that any individual goalie faced. To achieve this new metric we create smoothed nonlinear spatial maps of goalie performance based upon the shots they did face and then evaluate these goalies on the league average distribution of shots. These maps show the probability of a goalie giving up a goal from across the playing surface. We derive a general mathematical framework for the evaluation of a goalie‟s save percentage. Using data from the 2009-10 NHL regular season, we apply this new methodology and calculate our new defense independent goalie rating (DIGR) for each goalie that face more than 600 shots. Results of this evaluation are given and possible extensions of the methodology are discussed.