The number of players on a Major League roster is dictated by the
labor agreements worked out between players and management. According to
the current
rules, a team may have a maximum of 25 men on a roster from Opening Day
until August 31. After that, during the regular season teams may call
up additional personnel to the active roster, up to a maximum of 40
players. This number is seldom actually approached, however, with most
teams' September rosters peaking at around 30 players.
In the postseason, rosters are fixed at 25 men. Until 2007, teams could not replace players on their playoff rosters in the event of an injury and had to play out the series shorthanded. Starting in 2007, an injured player could be placed on the disabled list and replaced by another player not included on the initial 25-man roster, but the injured player is no longer available for the next round of the playoffs should his team advance due to his being on the DL.
In the postseason, rosters are fixed at 25 men. Until 2007, teams could not replace players on their playoff rosters in the event of an injury and had to play out the series shorthanded. Starting in 2007, an injured player could be placed on the disabled list and replaced by another player not included on the initial 25-man roster, but the injured player is no longer available for the next round of the playoffs should his team advance due to his being on the DL.