What is double rule?

Answer 1

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 that the batter will be awarded a double.

AnswerWhen the ball hits the ground in fair territory, then bounces over the wall.

It cannot be a homerun, and the fielder cannot get to the ball, so it is a "Ground Rule Double"- the runner goes to second base, and all base runners can advance two bases.

Correction.What is described above is actually an example of an Automatic Double. People who do not know the rules of Baseball have mistakenly called this a ground rule double. A ground rule double would be an award of a double that only applies to a specific ball park based on that park's quirky field. Currently there is no park in the MLB that has a ground rule double.