Ground rule double
A ground rule double is a baseball rule that awards two bases from the time of pitch to all baserunners including the batter-runner, as a result of the ball leaving play after being hit fairly and leaving the field under a condition of the ground rules in effect at the field where the game is being played. An automatic double is the term used to refer to a fairly hit ball leaving the field in circumstances that do not merit a home run, as described in Major League Baseball (MLB) rules 5.05(a)(6) through 5.05(a)(9). The automatic double (or rule-book double) is quite often mistakenly called a ground rule double.
While Major League Baseball has a set of universal ground rules that apply at all ballparks, none of these rules provide for an award of two bases to a runner. A true ground rule double thus is granted only when the ground rules of a specific park come into play—rules created to provide for unique playing conditions of that park. For example, ground rules govern the situation when a batted ball is lodged in the ivy at Wrigley Field or the walkways at Tropicana Field.
The far more commonly occurring automatic double results from the generally applicable MLB rules 5.05(a)(6) through 5.05(a)(9). These rules govern how to treat the batter (and any runners on base) when a batted ball is hit fair but passes out of the field of play or becomes artificially obstructed while in the field of play. For example, these rules cover balls that hit the ground in fair territory and land out of play, typically by bouncing over a fence or wall in the outfield. MLB rules also provide generically for the award of a double when a batted ball goes through or under a fence; and when it goes through or sticks in shrubbery or vines on the fence.
One of these MLB Rules (5.05(a)(9)) governs when fair fly balls are deflected into the stands by a fielder: for example, a fair fly ball deflected out of play by a fielder from a point within 250 feet of home plate is considered a double. This applied in an unusual play August 3, 2007 when Melky Cabrera of the New York Yankees hit a ball that ricocheted off Kansas City Royals pitcher Ryan Braun's foot and bounced into the stands in foul territory.
When two bases are awarded by either ground rules or the automatic rule, any baserunners ahead of the batter are entitled to advance two bases from their positions at the time of pitch. Only in the case of interference is the umpire vested with discretion to award more bases. The ground rule or automatic double frequently results in a runner at first base who appears to have been able to score on the batted ball nevertheless being returned to third base when the ball goes out of play.
In the early years of baseball, all batted balls that cleared the fence after a bounce in fair territory or on a fly were counted as home runs. The rule was changed by the American League prior to the 1930 season and subsequently by the National League on December 12, 1930. Notably, the pre-1930 rule includes most of Babe Ruth's career. Early baseball statistics do not differentiate between home runs that cleared the fence on a bounce compared to those that did not.