Ballbusting is causing pain to the testicles of the male for enjoyment reasons rather than for self defence reasons. Women enjoy it for the power they feel when they can so easily drop a male to the floor in great agony. They also find it amusing to see them sqirming and groaning while holding their scrotums from such a minor blow. Males seem to enjoy their own vulnerability when it comes to a woman exploiting it. Most men become erect at the thought of a woman controlling them by their testicles. (women always aim for the testicles for self defence which is also a turn on for many)
Her fascination in ballbusting was her interest in the male weakness in his testicles and wanted to experience the feelings of power over a man much stronger than herself. She looked for any reason to kick a man in the balls.