Apologies in advance if this is common knowledge. Until 1930, a ball that went over the wall after bouncing in fair territory was ruled a home run. I read this in one of those books of random trivia and confirmed on Wikipedia and various other Internet sites. Such a play isn't technically a "ground rule double" -- those are a result of the ball leaving the field of play due to a circumstance of the ground rules -- but a ball bouncing over the wall has come to be referred as such. Call it a "league rule double", or something similar.
The current application of the rule makes sense, considering changes to ballpark dimensions and the ball itself since the early 1900s. But the concept has always seemed peculiar. The ball goes over the wall and the hitter has to... stop at second base? Run until you're tagged out, right? Shouldn't a home run be awarded? I'm not endorsing a rule change, but merely thinking out loud and trying to make sense of it.
While growing up, the rule was always in effect in little league and high school ball. Yet there was never a special ground rule in place on fields which lacked an outfield wall, leading to more than a few instances of the coveted "groundball home run". It was always a blast playing on fields which the opposing team's grounds crew turned into a putting green. Outfielder positioning and overall offensive strategy changed based on whether a field had an outfield wall, and how far away that wall was from home plate. Few games were ever out of reach.
If the pre-1930 rule was suddenly re-implemented in MLB today, what kind of effect on the game would it have? Maybe teams would plan to move the walls back in stadiums or construct their own versions of the Green Monster. Speedy players would likely rise in demand, both for offensive and defensive reasons. The larger dimensions would allow players to run for days. One-skill slugging outfielders would probably decline in value, with plus defenders desired at all three outfield positions. Would players practice hitting one-hoppers over the wall?
Anyway, I found the news of this rule change intriguing and worth pondering for a few minutes. Enjoy this diagram of the Polo Grounds' dimensions, courtesy of BallparkTour.com.