Killer instinct goes a long way.
Also, [img]/images/graemlins/confused.gif[/img] at everyone who thinks MMA fighters are powerless without gloves?
http://www.youtube.com/watch?v=cwppgeQQ4sA
Bas Rutten trains like a madman, has been known to train so hard that he injures himself before fights, but ends up winning anyway. The man is also has a big killer instinct, and doesn't take much to get into a fight with you on hte street (watch the video to see what sets him off to break limbs) and has been in countless brawls in his country.