This is a baseball term which refers to the set of rules that apply to a specific ballpark. In Major League Baseball, every stadium and ballpark is a little different and requires a special set of rules to apply to all the various differences. There are a set of league-wide ground rules that must be followed at all stadiums. Beyond those rules, teams are allowed to set their own ground rules in so much as they do not violate league rules governing the park. An example of a ground rule is if the ball gets lost in the ivy on the back wall in Wrigley Field in Chicago, the hitter and all runners are awarded two bases.
The types of obstacles that must be accounted for in the ground rules include: dugouts, bullpens, on-deck circles, stadium walls, foul territory, press boxes, cameras, and many other irregularities. There is special consideration given to those teams who have a domed stadium. They are governed by an additional set of rules that they all must follow.