I've just been the recipient of ball busting by Mistress Capricious,

https://www.adultwork.com/ViewProfil...%2FSearch.asp]

As you can see on her Adult Works profile, she has a number of talents, and she excels at ball busting! She left me with a real pair of achers! She punches and knees hard, though she will do it softer if you prefer.
I also asked for a few other things, like face slapping and hair pulling, and she's good at that to, so I definitely recommend her.