In baseball a ground rule double is a hit that goes out of play (into the stands or out of the park) just as a home run, but on the bounce, having touched the ground. A home run must leave the playing field on the fly.

In addition to the usual ground rule double conditions, some parks have odd playing features that may constitute a ground rule double if invoked; the Hubert H. Humphrey Metrodome, for example, rules that a baseball caught in the Teflon roof is a ground rule double.