A sexual act involving two males. The first male gently cups his testicles with one hand, while using the other to lift the penis so as to have a space between the top of the scrotum and the underside of the the shaft of the penis. The second male then thrusts his hardened penis into this space. The first male releases his penis, creating a more tight space for the second penis to fill. The second male proceeds to fuck this space.
The first male may always opt to squeeze his entire package in between his hands, so that the male fucking the scrumdiddle may receive more pleasure.
Charlie: Hey Jim, wanna scrumdiddle after dinner?
Jim: FUCK YES I DO!
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.