In baseball, a double is the act of a batter striking the pitched ball and safely reaching second base without being called out by the umpire, without the benefit of a fielder's misplay (see error) or another runner being put out on a fielder's choice.
Typically, a double is a well-hit ball into the outfield that either finds the "gap" between the center fielder and one of the corner outfielders, bounces off the outfield wall and down into the field of play, or is hit up one of the two foul lines. To hit many doubles, one must have decent hitting skill and power; it also helps to run well enough to beat an outfield throw.
Doubles typically drive in runs from third base, second base, and even from first base at times. When total bases and slugging percentages are calculated, the number two is used for the calculation. The all-time leader in doubles is Tris Speaker, with 792.
A two-base hit awarded by an umpire when a batted ball is hit fairly and bounces out of play is referred to as a ground rule double. The batter is awarded second base and any runners advance two bases from the base they occupied at the time of the pitch. Prior to 1931, such hits were considered home runs. A two-base hit awarded because the batter hit into a special situation defined in the ground rules is also defined as a ground rule double. An example of this occurs where the rules of Wrigley Field (Chicago, Illinois) award a ground rule double if a batted ball hangs in the vines on the outfield bleacher wall. The rules of the Hubert H. Humphrey Metrodome (Minneapolis, Minnesota) award a ground rule double if the ball becomes stuck in the Teflon ceiling. (This has happened only once; Dave Kingman hit a ball into the ceiling during a 1984 game.)

Career

Earl Webb (1931) - 67
George Burns (1926) - 64
Joe Medwick (1936) - 64
Hank Greenberg (1934) - 63
Paul Waner (1932) - 62