Balls deep has two meanings, the first meaning is in the sexual way of getting your penis all the way in into a
vagina and only the balls are left outside, and the second meaning that it is used between homies is when you go really
hard into something
like doing a good hard workout and feeling it after.
First example in a sexual way: Yo bro I went balls
deep on her
sister last night.
Second example in a non-sexual way: Yo bro I went balls
deep on that workout and all my body hurting now.