GROUND RULE

n. 1. A rule in sports that is made especially for the grounds or place where a game is played. Usually used in the plural. There was such a big crowd at the baseball game, that the ground rules of the field were changed in case a ball went into the crowd. 2. A rule, usually not written, of what to do or how to act in case certain things happen. Usually used in the plural. When you go to a new school, you don't know tire ground rules of how you are supposed to behave.