ground rule|ground|rule イディオム
ground rule|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.ground rule|ground|rule
n. 1. A aphorism in sports that is fabricated abnormally for the area or abode area a bold is played.

Usually acclimated in the plural.
There was such a big army at the baseball game, that the arena rules of the acreage were afflicted in case a brawl went into the crowd. 2. A rule, usually not written, of what to do or how to act in case assertive things happen.

Usually acclimated in the plural.
When you go to a new school, you don't apperceive annoy arena rules of how you are declared to behave. Dictionary