I've seen blood in an IPSC match a few years ago. The guy tripped over the edge of a rise where you had to kick a door down and in the automatic reaction to prevent his gun from falling his face (nose) hit the ground. Lots of blood was flowing even though his nose wasn't apparently broken. His gun was still in his hand so he was not DQ'd!
That's the worst accident I've ever seen. Hockey, baseball, etc. well... that's a different story. I'm at the age now where I'm glad to be in the wimpy safe sport of practical shooting