Ouch! There are options you can use to prevent chafing. Things like lubricants, baby powder, sweat wicking synthetics, jock straps and tighty whitey underwear all provide relief.

What is the benefit of a jockstrap?

The purpose of the jock strap is to hold the male genitals in place and suppress excessive motion. That's not to say you can't get the same support any other way: a supportive pair of briefs may serve the same antibouncing purpose. The biggest benefit of the jock strap is the ability to add the protective cup.

Why am I chafing by my balls?

Testicular chafing is a flaking and redness of the skin on the scrotum. It is brought about through a combination of friction and heat. Cyclists are prone to it as are men who work outside in hot weather. Tight clothes can also contribute.