Holla is a well known term in the "gangster" world meaning Hello or How Do You Do? Front refers to a person or "homies" house or "hang out" spot. Put two together and it simplys means dropping by your friends(homies) house(hang out spot) just to say hello, maybe have a beer and fancy a game of criquette on the tube (television).
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.