I have seen a couple instances of bullet fragments coming back and hitting people, nothing serious.
Heck, when I shot bowling pins, that was par for the course. I learned really quickly why the older guys had bushy beards and wore aviator glasses.
I've seen a few ND's during competitions, though none causing injury. The most recent actually happened outside the range, and the guy responsible was not only unrepentant, he demanded his deposit back because he wasn't going to be allowed to shoot. Jeez.
Several years ago, a friend was running a bullseye shoot at an outdoor range when an unaffiliated person showed up. The guy asked if he could shoot, and my friend explained that the range was sequestered for the shoot. The guy then went to the line and loaded up. Before my friend could stop him, the guy put the gun to his head and took his own life.
The incident was at first reported as having occurred during the competition.