That is described as the “cumulative catch probability that fielders have been credited or debited with. So it’s a counting stat based on total number of fly balls that were in a catchable range. This, by definition, the left fielder in Fenway is at a disadvantage to almost every other left fielder in the game.Yes, statcast accounts for the wall in their outs above average which he is one of the the worst outfielders in baseball. the other metrics are based on stringers watching every play so that accounts for the wall now as well. for whatever reason benintinedi's speed has been getting worse every year.
If the ball falls into the fourth row of the bleachers in foul territory in LF in Fenway, OAA pretends the play didn’t exist. By contrast the left fielder in Oakland or Anaheim could be credited with a sliding catch against the wall on the same fly ball trajectory.
Also, “outs above average” would not account for the effect of Jackie Bradley’s tremendous range in CF on the number of balls caught by Benintendi.