Or running shorts...
They have a built in liner that works quite well when you wear the correct size.
Properly sized running shorts are great, I personally like the really short side spit ones, the hold the "tackle" and you still get some air circulation, and can go shirtless without worrying about a waistband of underwear or a jock showing.
I have a friend who would wear properly sized side split running shorts, but he would cut out the brief liner and wear a swimmers jock, it is definitely a hot look, though a little daring depending on where you run, and have to watch sitting down.