An enjoyable form of BDSM play whereby the male scrotum is exposed and beat and slapped repeatedly with a riding crop like the ass end of horse running the Kentucky Derby.
My mistress pulled my scrotum from my fly and gave me derby balls. The pleasure was incredible.

I feel like I’m ready to run for the triple crown after having my scrotum bashed in the most delightful session of derby balls last night.
by Eaton Holgoode February 7, 2018
Get the Derby Balls mug.