In reference to baseball, to give the Slap Ass, one must lower the arm to waist height with the forearm slightly elevated. On the approach of another teammate from behind, the wrist is bent back slightly and a quick tap is given on the ass.
This act of sportsmanship and encouragement is given following either a good play, a play that was ruined, or for just plain pep.
The slap ass is limited too, but does not exclude, coaches of other sports, as well as other sports players.
NOTE: This is the ONLY instance in which another male may slap another male's ass, and not be considered gay by fellow teammates. On-lookers, fans, and friends are not subject to this requirement, and thus may consider you gay.
Friend 1: Man, did you just see that awesome web gem
Friend 2: Yeah, he even got a slap ass afterwards.
Onlooker 1: Did you just see that guy give a slap ass to the other guy? I think they may be gay.
Onlooker 2: No, they aren't. They play baseball.
Onlooker 1: Ohhhhh.