Major League Baseball (MLB) has a set of
universal ground rules that apply at all ballparks, two of which award two bases to the batter and any baserunners: • A batted ball lodged in the roof above fair territory (unless outlined otherwise in the home park ground rules) • Any batted ball in fair territory that, in flight, strikes the facing of a lower wall and then bounds over a higher wall are ground rule doubles. Two bases can also be awarded per
home park ground rules—rules created to provide for unique playing conditions of a specific ballpark. For example, ground rules govern the situation when a batted ball is lodged in the
ivy at
Wrigley Field, or the walkways near the ceiling of
Tropicana Field, a domed stadium. 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. The 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. . MLB rule 5.05(a)(9) governs when fair fly balls are deflected into the stands by a fielder: "The batter becomes a runner when... Any fair fly ball is deflected by the fielder into the stands, or over the fence into foul territory, in which case the batter shall be entitled to advance to second base; but if deflected into the stands or over the fence in fair territory, the batter shall be entitled to a home run. However, should such a fair fly be deflected at a point less than from home plate, the batter shall be entitled to two bases only." ==History==