Ballbusting

Cock and ball torture (CBT) is a sexual activity involving application of pain or constriction to the male genitals. This may involve directly painful activities, such as genital piercing, wax play, genital spanking, squeezing, ball-busting, genital flogging, urethral play, tickle torture, erotic electrostimulation or even kicking. The recipient of such activities may receive direct physical pleasure via masochism, or emotional pleasure through erotic humiliation, or knowledge that the play is pleasing to a sadistic dominant. Many of these practices carry significant health risks.

"Ball-busting" is a form of CBT in which a man has his testicles kicked, kneed, punched or squeezed. In addition to its occasional role in BDSM pornography, Tamakeri (玉蹴り) (lit. ball-kicking) is a separate genre in Japan. Like many of the other activities in this article, it carries significant health risks, including the possibility of permanent damage to the testicles through testicular trauma.

A ball stretcher is a sex toy that is used to elongate the scrotum and provide a feeling of weight pulling the testicles away from the body. This can be particularly enjoyable for the wearer as it can make an orgasm more intense, as testicles are prevented from moving up. Intended to make one's testicles permanently hang much lower than before (if used regularly for extended periods of time), this sex toy can be potentially harmful to the male genitals as the circulation of blood can be easily cut off if over-tightened.

While leather stretchers are most common, other models consist of an assortment of steel rings that fastens with screws, causing additional but only mildly uncomfortable weight to the wearer's testicles. The length of the stretcher may vary from 1-4 inches, and the steel models can weigh as much as five pounds or more. A more dangerous type of ball stretcher can be home-made simply by wrapping rope or string around one's scrotum until it is eventually stretched to the desired length.

...
Wikipedia