When one wears no underwear beneath his trousers
e.g Did you see Steves arse, he was free balling so hard.
Or, In the sport of cricket one is said to "free ball" when they wear no box (protects genitals) whilst batting.
Carl: are you alrite dude?
Hank: Na man I took one to the balls
Carl: did your box shatter?
Hank: Dude I was free balling