Derived from an older German last name, "Baumgartner", meaning gardener of tree groves, the altered name "Bumgardner" is a variation that is more similarly meaning that of a sexually active person who trains and sells prostitutes similar to gardening as a pimp.
It is said of the situation where a person has the bad luck to make contact with his testicles against an undefined surface or object, intentioned or not.
Given the nature of the word, it is more appropriate to design cases where the interaction is made with a moving object, for example, a ball.
Although it is extremely painful for the victim, it tends to be considerably funny to people who witness it.
Today in the baseball game the pitcher took a nutshot; the baseball hit him in the nuts.
Man, I just watched the funniest nutshot video ever.