I'll never forget the Soviet diver who died after hitting his head on the platform at the University Games in Edmonton back in 1983:
https://en.wikipedia.org/wiki/Sergei_Chalibashvili
Apparently, he's the only competitor to ever die from an accident like that in a major competition. I remember there being a lot of discussion as to whether or not platform diving should even continue to be a sport after that happened.
Greg Louganis, one of the greatest divers ever, smacked his head on the springboard at the Seoul Olympics, but he only suffered a concussion and was able to come back and still won the gold.