I remember watching a UFC fight where a guy got injured during a takedown. No one really realised until he got up, then the ref (Herb, I think?) stopped the fight. At first, no one quite knew why, then when the fighter was sitting on the stool, the doctor shifted his leg and the whole bottom half of his leg seemed to move completely independently of the top half. A really, really bad dislocation. I remember being thoroughly grossed out by it... But it's a vague memory and it may not have been as bad as I remember.
Failing that, Mir snapping Nog's arm was bad, bad, bad. So bad. I remember when they were rolling and Mir finally secured the position, I suddenly realised that Nog wasn't going to tap, and that Mir is not the kind of guy who has many fucks to give, so we were about to see a broken bone... Honestly makes me a little queasy just thinking about it.