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Playoff Goaltending and "Hot" Goalies

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I have a friend who is a big believer in "hot" goaltending in the playoffs.  In a sense, he's not wrong - the team with the goaltender who puts up the best apparent performance is usually the team that wins a series.  I think this is the best way to describe what my friend sees:

 

GP SV%
1 0.870
2 0.869
3 0.876
4 0.885
5 0.895
6 0.899
7 0.900
8 0.902
9 0.905
10 0.904
11-15 0.908
16-19 0.912
20-22 0.917
23-26 0.922

 

Basically, the higher your save percentage, the more games you'll play.  The guys who win the cup are the ones who play the best.  I find this table to be an instructive way of looking at the issue:

 

Save Pct Reg Season Playoffs
Cup Winners 901 919
Others 902 906

 

So the teams that win are the ones whose goalies get hot in the playoffs - the guys who up their level of play, the clutch goalies. Unfortunately, the clutch goalies are indistinguishable from the pumpkins!  We've got two sets of goalies who play no differently during the regular season, but all of a sudden one group starts playing well - how can we figure out ahead of time which group our goalie is going to fall into?

As I've stressed before, the best measure of a goalie's true talent is his save percentage, preferably over 4+ seasons or an entire career.  When we look at the relationship between regular season save percentage and playoff save percentage, we get the following:

 

Reg->Play Sv% Regress R^2
Single-Season 61 16
Career 34 57

 

Single-season save percentage is fairly meaningless for predicting a goalie's performance in that season's playoffs.  A .920 goalie gets regressed down to a .914 one, making him just 1/10th of a win better over a seven-game series than a league-average goalie.  Because goalies play so few games in the playoffs, their performance is heavily luck-driven.  One bad bounce or one bad goal and their season can be over.

At the career level, regular season performance is actually a very good predictor of how a goalie's going to do over the course of 20+ games in the playoffs.  Unfortunately, the average goaltender plays just seven games in the playoffs in a given season, and the predictive value of career save percentage isn't much better than this year's save percentage. 

So yes, you need a 'hot' goalie to win the playoffs.  It's just not possible to figure out who's going to be 'hot' until after the fact.