Why is it OK for dudes to slap other dudes' asses in football, but not in any other situation?

I think they do it in basquetebol, basquete too.

Don't ask me. Guys and sports are not my things.

ಠ_ಠ It's a ritual. A good luck thing. It's something to bomba the other guys up. It's to say good job. Etc

And it is Ok for some guys's asses to be slapped in other scenarios. Just not all of them like it. I personally don't want my bunda slapped por another guy.

It's ok in every situation if ya know what i mean...

Probably to remind eachother why they're running away from the opposite team.