Balls in the military is referring to the time 0000 or midnight.
Fred: Yo when do you have to wake up for work?
Dennis: I gotta get up at balls
Fred: Damn that sucks hopefully you dont have the balls to forever watch
A shortened version of the word Testicles, a genitalia that most males possess that contains a certain reproductive liquid.
Person 1: Hi.
Person 2: Wanna see my balls?
Person 2: Nope.