Short-season

Short-season refers to a league that does not start play in the spring, like Major League Baseball or most other professional leagues, instead beginning play in late June. This is partly to take advantage of better weather, but mainly to allow newly signed players who have just graduated from high school or college to join the team at the beginning of the season. Their starting dates were originally based in part on the date of the annual amateur draft when that event was still in June.

A short-season league would play up to 70 games, while full-season affiliated leagues play about 140 - typically, the higher the classification the slightly longer the season. Within the hierarchy of Organized Baseball, with fewer games and players just beginning their professional careers, they were in the lower classifications.

However, MLB eliminated affiliated short-season baseball, except what are known as Complex Leagues, from its feeder system in its 2021 Minor League Reorganization.

Before the shuffle, its short-season leagues included the Class A-Short Season New York-Pennsylvania League and the Northwest League, the Rookie-Advanced Appalachian League and Pioneer League), the complex-based Arizona League and Gulf Coast League, and the foreign-based Dominican Summer League. Another non-domestic circuit, the Venezuelan Summer League, had folded after the 2015 season.

The four circuits affected by the 2021 down-sizing were: the New York-Pennsylvania League, which was dissolved but with three of its 14 teams moving into an affiliated full-season league; the Northwest League, which was reduced from eight to six teams and moved up the full-season classification now known as High-A; the Appalachian League, which was dissolved as an affiliated league but reincarnated, under the same brand, as a summer collegiate league; and the Pioneer League, which was converted to an independent professional league.

The Arizona and Gulf Coast leagues were rebranded in the reorganization as, respectively, the Arizona Complex League and the Florida Complex League.

The Northern League, which shut down after the 1971 season, was also a short-season league for much of its existence. Four largely unrelated circuits used the name in roughly the same geographic footprint as far back as 1902, with the last forming in 1933 and playing continuously through 1971 except during World War II. The name, however, continues: An independent pro league used it from 1993 through 2010, and a summer collegiate league that had been founded in 2010 as the Midwest Collegiate League rebranded to it in 2022.

There are still short-season leagues in independent ball, mainly for weather considerations. The Canadian-American Association is an example.