Goals Saved Above Expected (GSAx)
A goaltending metric that measures how many goals a goalie has saved compared to the expected goals total of the shots they faced. Positive GSAx means the goalie saved more than expected.
Goals Saved Above Expected (GSAx) is the premier goaltender evaluation metric in modern hockey analytics. Traditional save percentage treats all shots equally, but a save on a point shot from 60 feet is far easier than a save on a one-timer from the slot. GSAx accounts for this by comparing each shot's expected goal value to the actual result.
The calculation is straightforward: sum up the xG of every shot a goalie faces (this is the total expected goals against), then subtract the actual goals allowed. If a goalie faces 50 xG worth of shots in a season and allows only 40 goals, their GSAx is +10.0 -- they saved 10 more goals than an average goalie would have facing the same shots.
GSAx has largely replaced save percentage as the primary goalie evaluation tool because it accounts for shot quality. A goalie behind a poor defensive team will face more dangerous shots and is expected to allow more goals. GSAx levels the playing field, isolating the goalie's individual performance from the team defense in front of them. Elite goalies typically post 15-30 GSAx over a full season.
Formula
GSAx = Expected Goals Against - Actual Goals Against Expected GA = sum of xG for all shots faced Positive GSAx = saved more than expected (good) Negative GSAx = allowed more than expected (bad)
Frequently Asked Questions
What is a good GSAx for an NHL goalie?
An average goalie has roughly 0 GSAx by definition. Above +10 GSAx for a full season is very good, and above +20 is elite (Vezina Trophy caliber). Negative GSAx indicates the goalie allowed more goals than expected based on shot quality.
How is GSAx better than save percentage?
Save percentage treats all shots equally -- a routine glove save from the point counts the same as a miraculous cross-crease stop. GSAx weights each save by the shot's difficulty (xG value), providing a far more accurate measure of goalie skill. It also controls for the quality of defense in front of the goalie.
Does GSAx account for the team defense?
Indirectly, yes. By measuring against expected goals (which reflect shot quality), GSAx accounts for the fact that some goalies face harder shots than others. A goalie behind a bad defense will face more high-danger shots but is "expected" to allow more goals -- GSAx measures performance relative to that expectation.
How does GSAx feed into goalie GAR?
Hockey Alchemy's goalie GAR is directly based on GSAx. The goalie's GSAx value is adjusted relative to a replacement-level goalie (not an average goalie), then converted to a GAR value. This allows goalies to be compared on the same scale as skaters.