When you pull your pants down to piss, and one of your testicles hangs out of your pants, and the other stays in your pants. Can be slightly painful/uncomfortable if wearing very tight pants.
Person 1: Man, I hate having to take a piss because I always have a hang ball.
Person 2: Yeah, I feel your pain.
In baseball, a hanging curve is generally thought to be a very hittable pitch, usually implying the ease in which a player can hit a home run. A hanging curve is an easy task in which the chances of success are high.
"All you have to do is show up, shake a few hands, and we'll pay you $1000."
"Sounds like a hanging curve ball!"