Measuring Goalkeepers: The Limitations of Goals - xGoals by Bill Reno

Last month we took a look at how bad the Goals Against Average (GAA) stat is for evaluating goalkeepers and how the save percentage (S%) is slightly better. To show the inefficiencies of the GAA and S%, I compared them to ASA’s own unique stat of Goals Minus Expected Goals (GmxG). The GmxG looks at where shots are taken, calculating the likelihood of a shot going in from that distance and angle to goal, which ends up telling us if a goalkeeper is giving up too many goals given the circumstances. This is great for a couple of reasons, the main one being that we have a more accurate reading on shots on goal than the ol’ shot percentage. If one goalkeeper consistently sees shots from distance while another is routinely left out to dry by his defense, the GmxG will let us know how many goals each goalkeeper should be conceding even if their SOG and goals are similar. However there are some shortcomings with any stat and the GmxG isn’t any different.

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