The moment in time when you need to poop and you know for a fact if you do it now it will be a good poop. Waiting past this window results in a less then perfect poop, Usually with not getting it all out or straining harder than you would have had to if you had done it during your O.P.W.
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.