Trench warfare is fighting between two opposite sides with soldiers dug into ditches on either side with "No Man's Land" inbetween. It usually consists of soldiers, sometimes tanks, and usually artillery. One side would send wave after wave into No Man's Land untill they gave up or the opposing Trench was overrun. Trench warfare was first used in World War 1 and continued as a style of fighting for years to come.
Charles V: Men, You will be sent into Trench Warfare in France against the Germans.
Kaiser Wilhelm: We will also use Trench Warfare!
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.