This is a short video of a man participating in a keg-tossing competition when one of the kegs he throws bounces off the pole he's trying to toss it over and comes down on the back of the head, knocking him out cold. Thankfully, the man was "sent home from the hospital with a clean bill of health." And, presumably, a doctor's recommendation to retire from keg tossing.
Keep going for the video.
Thanks to Zootghost, who agrees that's why you should only roll kegs.