Triple-A teams' main purpose is to prepare players for the Major Leagues. ESPN wrote in 2010: Both young players and veterans play for Triple-A teams: Players on the 40-man roster of a major league team are eligible for promotion to the major league club once the major league roster expands on September 1. For teams in contention for the postseason, these players create the flexibility needed to rest regular starters in late regular-season games. For those not in contention, using such players lets the teams evaluate them under game conditions.
Leagues
Teams at this level are divided into three leagues: the International League, the Pacific Coast League, and the MLB-independent Mexican League. The Mexican League fields teams throughout Mexico. The International League traditionally fielded teams in the Northeastern United States, and now fields teams in the Midwest and South as well. The Pacific Coast League originally fielded teams on the West Coast, but now fields teams throughout the western part of the United States, as far east as Nashville, Tennessee. For much of the 20th century, the American Association, which consisted of teams in the Midwestern United States, was also at this level, but it disbanded in 1997 and its teams were divided among the IL and PCL. Each of the 30 Major League Baseball teams has an affiliation with one Triple-A team in the United States. However, Mexican Triple-A teams are not included in the organized farm team system.
Current teams
International League
Pacific Coast League
Mexican League
Triple-A All-Star Game
The Triple-A All-Star Game is a single game held between the two affiliated Triple-A leagues—the International League and the Pacific Coast League. Each league fields a team composed of the top players in their respective leagues as voted on by fans, the media, and each club's field manager and general manager. The event has taken place every year since 1988 when the first Triple-A All-Star Game was played in Buffalo, New York. Prior to 1998, a team of American League-affiliated Triple-A All-Stars faced off against a team of National League-affiliated Triple-A All-Stars. Traditionally, the game has taken place on the day after the mid-summer Major League Baseball All-Star Game. The game is meant to mark a symbolic halfway-point in the season. Both Triple-A leagues share a common All-Star break, with no regular-season games scheduled for two days before the All-Star Game itself. Some additional events, such as the All-Star Fan Fest and Triple-A Home Run Derby, take place each year during this break in the regular season.
As a part of professional baseball's pace of play initiatives implemented in 2015, 20-second pitch clocks entered use at Triple-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 included beginning extra innings with a runner on second base and limiting teams to six mound visits during a nine-inning game. For the 2019 season, the number of mound visits was reduced to five, and pitchers were required to face a minimum of three consecutive batters unless the side is retired or the pitcher becomes injured and is unable to continue playing.