I watched a good friend get hit in the junk with a tennis ball (thrown by one of my other good friends at close range), a week later, the friend who got hit was at the Bears game and couldn't even climb the stairs at soldier field, had to be rushed to the hospital and ended up having one of his nuts removed since it had been twisted around the other one and the bottom one had died.
I was a 100% cup wearer when I played baseball, probably because I was a catcher, but I think I would have anyway, nothing worse than getting hit in the nuts.