Monday, June 25, 2007

Is It Harder To Face Fewer Shots?

There is a debate over whether save percentage is influenced by the number of shots faced. Some argue that the more shots a goalie faces, the more difficult it is to save them. This position was taken by Klein and Reif in their influential Hockey Compendium, and led to their Goaltender Perseverance stat that rewards goalies who face more shots per game. Others maintain the opposite, that goalies who face fewer shots have a more difficult task. This is because it is harder to stay focused, and their teammates tend to prevent the long, easy shots that other goalies face. This has often been used in support of Martin Brodeur, including in comments posted at this blog.

Neither of these viewpoints are correct. In an article on Puckerings.com, Ian Fyffe dismantled Klein and Reif's viewpoint and argued that Perseverance is meaningless. There is very little correlation between shots faced and save percentage, and the evidence is that shots faced are overwhelmingly a function of the team, rather than the goaltender. To further investigate this finding, I have looked at the top save percentage seasons of the save percentage era, which began in 1983 when the NHL began officially publishing shot totals. My findings supported Fyffe's, that save percentage appears to be independent of the number of shots faced, and that goalies can have outstanding save percentages both when facing many shots per game and when facing very few.

The average number of shots faced by goalies who had save percentages of .925 or better was 28.4 shots per game. The top 4 seasons were all by goalies facing fewer than 30 shots per game. In fact, the only goalies to face 30 or more shots and stop at least 92.5% of them in at least 50 games were Theodore, Luongo, and Hasek (3 times). Hasek is bringing up the average significantly; take him out, and the average shots against per game for the top goalies falls under 28 per game.

Several goalies made the list despite facing 26 shots or less, including Brodeur's .927 in 1996-97. Others were Kiprusoff (.933), Turco (.932), Cechmanek (.925), Tugnutt (.925), and Roy (.925).

That is just absolute save percentage, however. Save percentages have gone up and down with scoring levels in the NHL, which is why there were no 1980s goaltenders on that list. Perhaps a better way to look at it is through relative save percentage, which is save percentage divided by the league average save percentage for that season. Looking at the top 30 in relative save percentage (none of whom, of course, are Martin Brodeur), the goalies faced almost exactly a league average number of shots, and 10 of them faced 2 or more shots less than league average, including the top two (Bob Froese in 1986 and Dominik Hasek in 1994).

This list is not dominated with goalies that face a lot of shots. Of the top 30 in relative save percentage, only a few seasons fit the "Luongo" mold (lots of shots faced on a weak team): John Vanbiesbrouck on Florida in 1994, Bob Essensa on Winnipeg in 1992, Jose Theodore for Montreal in 2002, and Dominik Hasek several times on the Buffalo Sabres. Most of the goalies played on good teams.

The evidence suggests that save percentage is largely independent of the number of shots faced, and that shot quality is a more significant variable than the number of shots against. Facing a high or a low number of shots is therefore no excuse for a goaltender.