I was involved in a few situations like that in the army. Our policy was more or less: If it was a group of guys and our/my buddy was in trouble, then we'd probably help out as no one deserves a "group ass whoopin". That's just unfair. If it was just another individual, then our/my buddy was probably being a drunken a-hole and deserved it. In that case, I/we let nature take it's course unless it looked like he was totally getting his ass kicked or the cops were called and we needed to get his drunken ass out of there (saves on paperwork for all concerned
).