A violent guy hired to kill, intimidate or beat people for money, usually looks like a pugilist, wears agressive clothes (punk style, rocker style, gangsta style or like a bodyguard) and a fuckin' attitude that can intimidate anyone just to look at him.
You: Hey man, I will pay you 200 bucks to rough that stupid Bully that beated up my lil' brother!
5 minutes later...
Enforcer: This is from a friend you've fucked!!! (and he beats him in da face)
Bully (nose bleeding): No wait man! this must be a mistake =O !!!
Enforcer: Let's make this motherfucker pay!!! (and he starts to punchin' him so hard that you will feel pity... no wait, KEEP BEATING HIM :D!!)