Ground rules are just that - local (in the extreme) rules to deal with the grounds. Not quite sand lot, but they can be close.
I've called a few dome games where the dome came down fairly low over the infield and rather sharply over foul territory and the outside wall was just a few feet behind the backstop (which was really just a net).
Ground rules were if a batted ball contacted the dome roof or infrastructure:
1) Over the outfield - live ball, play on, can be caught as a fly ball.
2) Over the infield - dead ball, no pitch (do over).
3) Over foul territory or DBT - foul ball.
I hadn't thought about a ground rule double - nice touch - that would sure cause some discussion!
