Short season refers to a form of Minor League Baseball in which only 75 games are played each season, as opposed to the typical 140 games for an affiliated minor league at a higher level. Four leagues play short-season baseball: the New York-Penn League and the Northwest League play at a level designated "Short Season Class A", while the Appalachian League and Pioneer League are designated as "Advanced Rookie" (a step higher than the lowest level of Minor League Baseball, the spring training-complex-based Rookie Leagues, which play an even shorter 60-game schedule). The seasons start in June and end in early September, beginning shortly after the end of the high school and college baseball seasons, allowing Major League Baseball franchises to assign newly signed players to their affiliates at an appropriate developmental level.
Teams in short-season leagues are generally in small-to-medium-sized cities, although exceptions exist—one team is in Vancouver (the only Canadian team currently in the affiliated minor leagues), another is in the Seattle suburb of Everett, Washington, and two are in New York City, each affiliated with one of that city's MLB teams. Of the 30 MLB clubs, 13 field teams in Short Season Class A only, 8 clubs field their top short-season teams in the Rookie Advanced leagues, and 9 clubs have affiliates at both levels.
For many players, this is the first time they have ever used wooden baseball bats, because aluminum bats are most common in the amateur game, as well as the first time they have played every day for a prolonged basis, as amateur competitions typically regulate the number of games played in a week. (These are not always true for those who have played MLB-sanctioned, but amateur, collegiate summer baseball prior to turning professional.) Players are permitted to use certain approved composite bats at this classification, to help them make the transition from aluminum to wood bats.