A fight between unfriendly opponents; either a fight with an unfriendly opponent or a fight with an opponent who doesn't bare any unfriendliness whatsoever.
Brock Lesnar vs. Frank Mir in UFC 100, is one of the worst Grudge Matches in UFC history. After the fight, Brock (Overly confident that he won) screams at the camera and Franks face. He even tells Joe Rogan that he would rather drink Coolers light instead of bud-light (Because Coolers Light ain't paying him), and he'll "do" his wife one UFC 100 is over. Eventually, he apologies about his actions next morning in an interview.