When an individual is having their ass eaten out and suddenly expels fecal matter from the stimulation of the sciatic nerve (main butt nerve), which then causes them to vomit as a chain reaction. Then, the individual underneath them performing the oral sex comes into contact with the feces and vomit.
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.