In football analytics, different companies use different names for similar ideas. StatsBomb uses Post-Shot Expected Goals (PsXG), while Stats Perform uses Expected Goals on Target (xGOT).
Even though the models are built differently, they both do the same thing: they help us understand how likely a shot is to turn into a goal once it’s taken and help measure how well goalkeepers perform.
What is Post-Shot Expected Goals (PsXG)?
Post-Shot Expected Goals (PsXG) by StatsBomb is very similar to xGOT from Stats Perform. Both measure how likely a shot is to become a goal after the ball is hit.
- PsXG looks at how well the shot was taken. For example, a shot aimed at the top corner is more likely to score (and gets a higher PsXG) than one aimed straight at the goalkeeper.
- This helps us see how good a player’s finishing is or how hard the shot was for the goalkeeper to save.
Measuring Goalkeeper Performance: Goals Saved Above Average (GSAA)
Goals Saved Above Average (GSAA) is a way to measure how well a goalkeeper is performing compared to others. It looks at how many goals they saved based on the quality of shots they faced.
- If a goalkeeper has a positive GSAA: It means they’ve saved more goals than expected, meaning they’re doing a great job.
- If a goalkeeper has a negative GSAA: It means they’re letting in more goals than they should, meaning they’re underperforming.
How is GSAA Calculated?
You can calculate GSAA by comparing the PsXG (or xGOT) of the shots the goalkeeper faced with the actual number of goals they conceded:
- GSAA = PsXG conceded – Goals conceded
This tells us how many extra goals a goalkeeper has saved compared to what we would expect.
Example of PsXG and GSAA
Let’s say a goalkeeper faces shots with a PsXG of 8.0, meaning these shots should have resulted in 8 goals. However, the goalkeeper only concedes 6 goals.
- GSAA = 8.0 (PsXG) – 6 (Goals conceded) = +2.0
This means the goalkeeper has saved 2 extra goals, showing they’re performing better than average.
Conclusion
Though Post-Shot Expected Goals (PsXG) by StatsBomb and xGOT by Stats Perform are built differently, they both help us understand how good a shot was after it was taken.
By using these metrics, we can calculate Goals Saved Above Average (GSAA) to see if a goalkeeper is saving more or fewer goals than expected. This helps us understand both shooting and goalkeeping performance in a much clearer way.