A term in baseball that refers to a group of starting pitchers on the active roster who rotate their appearances in games in a predetermined order.
A baseball team's pitching rotation commonly consists of five starting pitchers. The reason behind a rotation is due to the need for pitchers to rest in between starts. Because of the number of innings a starting pitcher typically throws, pitchers in the rotation usually need three or four days rest before they can pitch again and remain as effective. In most cases, a team's best pitcher, or "ace" will pitch first in the rotation, with the weaker pitchers in the group given position in descending order. Most often the starting rotation will have a mix of right-handed and left-handed pitchers, as managers have the option of changing the rotation if they feel a particular pitcher has an advantage or an edge over the team they will face next. The starting rotation can change over the course of a season, although only members of the current active team roster can join the rotation when a spot becomes available.