A popular word of the 1990s that refers to women or men who are dumb or easily manipulated (not to be confused with chickenhead which means whore/town slut)
Larry Birkhead (Anna Nicole Smith Baby Daddy) giving Howard K Stern (Anna Nicole Smith lawyer/all around bitch) a blow job...viola the birkhead is born.
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.