Noun
(baseball) a special rule (as in baseball) dealing with situations that arise due to the nature of the playing grounds
Source: WordNetA batted ball that hits the ground (in fair territory) and bounces out of play is not a home run, but an "automatic double" in most stadiums (colloquially called a ground rule double ). Source: Internet
In fact, the corner of the south end zone was literally in the visiting baseball team's dugout, which was filled with pads for safety, and required a special ground rule that sliced off that corner of the end zone. Source: Internet
However, this is superseded by the "ground rule", which provides automatic doubles (when a ball-in-play hits the ground first then leaves the playing field) and home runs (when a ball-in-play leaves the playing field without ever touching the ground). Source: Internet