Double-A (or Class AA) is the second highest level of play in Minor League Baseball (MiLB) in the United States after Triple-A. There are thirty Double-A teams in three leagues at this classification: the Eastern League, Southern League, and Texas League. The modern Double-A classification was created in 1946 with the renaming of Class A1, which then contained the Texas League and the Southern Association. After the Southern Association disbanded in 1961, the Eastern League and the original South Atlantic "Sally" League were bumped up to Double-A in the 1963 minor league reorganization. The Sally League changed its name to the Southern League in 1964.
The Double-A classification usually hosts developing players that have been part of professional baseball for only a couple of years. These players can get to the Double-A level by earning a promotion from any of the Single-A or Rookie leagues. Players often advance directly to the Major League Baseball from this level, as the level of competition is higher. Because they are still advancing in their careers, the average talent level of Double-A may be higher than in Triple-A, which has minor and major league veterans who have been in the minor league system for a longer period of time and may have stagnated. A small handful of players might be placed in Double-A to start, usually veterans from foreign leagues or top prospects out of college. The step up to the Double-A level can be one of the hardest promotions for such players because it is the level at which pitchers need to have a good off-speed pitch in their repertoires. 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. Major league teams sometimes send players to play at the Double-A level to rehabilitate from injuries.
Because players are not moving back and forth from the major leagues at this level, the rosters tend to be more stable. Fans of Double-A teams have a longer amount of time to get acquainted with the players, which helps create a better relationship between the team and its fans.
Unlike the major league and the Triple-A level, all three Double-A leagues have their season divided into two parts, after the Eastern League announced that it would move to that system starting in 2019. One team may clinch a spot in the playoffs by winning the division in first half of the season. The teams' records are then cleared and another team will also clinch a playoff slot during the second half. Wild cards are used to fill out the remaining teams. Usually, four teams qualify for the league playoffs. This system is used at the Class A level as well.
Each of the three leagues holds its own midseason All-Star Game. From 1991 to 2002, the three combined to hold the Double-A All-Star Game between teams of American League-affiliated All-Stars and National League-affiliated All-Stars.
As a part of professional baseball's pace-of-play initiatives implemented in 2015, 20-second pitch clocks entered use at Double-A stadiums in 2015. In 2018, the time was shortened to 15 seconds when no runners are on base. Other significant changes implemented in 2018 include beginning extra innings with a runner on second base and limiting teams to eight mound visits during a nine-inning game. Beginning in 2019, the number of mound visits is reduced to seven, and pitchers are required to face a minimum of three consecutive batters until the side is retired or the pitcher becomes injured and is unable to continue playing.
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