Quoted from DeeGor:
I gave this some thought and tried using a little felt pad that is used on cabinet doors. It works pretty well, and when you lift the playfield the back of it actually dips down, so you don't run into issues with it knocking it off the wall.
Thanks, as always! Yeah, seems to have completely fixed the issue, though maybe looks a tiny bit hokey (but you can't really see/notice it unless you are looking for it). I used 2 pieces since I think sometimes it hits the upper "space" too. On hand I just had some felt that you would use on the bottom of chairs for wood floors, which is pretty thick. And you are correct...when pulling the playfield out, it dips down so completely misses the felt. You could put most any thickness on the wall there and you won't have clearance issues.