1) A female who gains power over a male by causing pain to his testicles (commonly "nuts"). Although it can include any kind of "nut" attack. The female most often employs her legs for the task, because of their relative proximity to the groin, and because the legs of a female have the needed stregnth to hurt a male without injuring him.
2) A female who humiliates, belittles, injures, chastises, dihabilitates, or otherwise causes distress to a man through non-physical means.
1) Guys ignore Amy's reputation as a ballbuster when they see her nice legs; at least until she kicks them in the nuts.
2) "That Amy is a real ballbuster; not only did she kick me in the nuts under the table, she used my weakened state to make me agree to her plan."