Paintball is a game in which people on two teams shoot at each other with guns that fire small round capsules of paint. If the paint hits you, you are “out,” or you lose a life, depending on the rules. People wear masks and padded clothes; the paint is meant to mark you, not to hurt you badly, though it can sting. The same word is also the little ball of paint itself, and people use it as a verb: to paintball means to play this game. It is a hobby and a party activity more than a school sport, and the tone is informal. In English the game-name and the pellet share one word; you tell them apart from the sentence.