Double-A (officially Class AA[1]) is the second-highest level of play in Minor League Baseball in the United States since 1946, below only Triple-A.
[2] Previously, Class A had been the highest level, predating the establishment of the National Association of Professional Baseball Leagues—the formal name of Minor League Baseball—in 1901.
[4] The Double-A classification usually hosts developing players that have been part of professional baseball for only a couple of years.
In addition, it is the level where fastball-only hitters need to learn how to hit off-speed pitches, or their hopes of advancing to the majors will diminish.
[6] Because players are not often moved back and forth from their major league parent club as often happens in Triple-A, the rosters of Double-A teams tend to be more stable.
[42][43] After the start of the 2021 minor league season was delayed by a month,[44] team schedules were released without a break for an all-star game.
Other significant changes implemented in 2018 included beginning extra innings with a runner on second base and limiting teams to eight mound visits during a nine-inning game.