Expected Saves (xS)
Meaning
Number of saves that would be expected from an average goalkeeper.
Equivalent to expected goals Expected Goals, where each shot on target is attributed a probability.
Calculation
The basic principle is the same as for the Expected Goals.
The probability of a shot being saved is determined for each throw on target using the location, type of throw, shooting speed, location on goal where the ball goes to and other variables. These values can be added up over one or more games and compared with the number of saves actually made.
Some models are very simple and use just the raw shooting area more advanced ones use more detailed data and machine learning approaches. As usual for save metrics shots missing the goal are not taken into account.
Interpretation
A goalkeeper performed better than expected if his number of actual saves is higher than expected. The higher the difference, the better.
Is more accurate and fairer than the normal save rate or the net save percentage due to the consideration of the difficulty of the save. However, adjusted save percentage is even more meaningful as it adjusts for what shots the defence allowed.