Ground rules are any particular rules that apply to a stadium or ball park. Do to different dimensions in ball parks there are different rules at each field as to when a ball is out of play.
A ground rule double is when a batted ball is ruled fair by the umpires and the ball bounces and goes over or is touched by a player and goes over an outfield wall. In this case, the umpires rule...
Previous submitter's answer: Yes. Only at Fenway Park in Boston. Fenway's Green Monster is the home of baseball's only in-play ladder, which extends from the upper-left corner of the old scoreboard...