Why do you have to wear a jockstrap under your baseball pants?

Answer 1

Baseball is considered a full contact sport. There are many times that you can be hit in the groin. They normally require guys to wear them so they have a higher chance of not getting injured.

***

You'd be wise to fit a cup in there somewhere too because foul tips and base runners inevitably make body contact in usually the most sensitive places.

Answer 2

Boys can wear a jockstrap to hold a protective cup in place, which protects you from a direct hit in the genitals. Or, a boy can wear a jockstrap just for support, to keep everything from bouncing and moving while he runs or works out.