Most Mixed Martial Artists enter match-ups with the mindset of the fight being a professional matter rather than a means of settling a personal vendetta. However, bouts occasionally come with bad blood between the involved participants and in the blink of an eye things can turn nasty. While boxing has its fair share of ugly incidents, the UFC is not without its own blemishes when it comes to competitors taking things a step or two over the line based on genuine dislike of a peer. Even as recently as this weekend, Wanderlei Silva and Chael Sonnen nearly threw down outside of the Octagon. (Photos by USA Today Sports Images)