Clubs normally have a 25-man active Major League roster but are allowed to recall one additional player who is on the 40-man roster to serve as the 26th member for the day of a doubleheader. That player accrues one day of MLB service time and is returned to the Minor Leagues following the completion of the doubleheader.
Players who are optioned to the Minor Leagues typically must remain there for a minimum of 10 days before they are eligible to be recalled to the Major League roster, but if a player is serving as the 26th man for a doubleheader or replacing a player who has been placed on the injured list, he can be recalled without having spent a minimum of 10 days in the Minors after being optioned.
Teams also are permitted to call up a 26th man on days when they are completing a previously suspended game and have another game scheduled after that, but the 26th man is only permitted to play in the regularly scheduled game that day, not the contest that was previously suspended.
On Sept. 1, teams can carry up to 40 players on their active roster until the start of postseason play, at which point the maximum reverts back to 25. All players added to the active roster during this period must be on the 40-man roster.
The Yankees optioned outfielder Mike Tauchman to Triple-A on May 13, 2019, but recalled him two days later to serve as the 26th man for their doubleheader against the Orioles. Tauchman started both games of the doubleheader, collecting an RBI single in Game 1, before being optioned back to Triple-A.
Impending rule changes that will go into effect at the start of the 2020 season
Beginning in 2020, the roster size from Opening Day through Aug. 31 (and during the postseason) will increase from 25 to 26, with the minimum number of players on the roster increasing from 24 to 25, and roster sizes for doubleheaders increasing from 26 to 27. The minimum number of days a player will need to remain in the Minors after being optioned will increase from 10 to 15, with the same exceptions in play.
The 40-man active roster for September will be eliminated. From Sept. 1 through the end of the regular season, all clubs must carry 28 players.
Furthermore, the number of pitchers a club can carry on the active roster will be capped (maximum number TBD). To adhere to that rule, clubs will have to designate each player as either a pitcher or a position player prior to each player's first day on the active roster for a given season. That designation cannot change for the remainder of the season.
Position players will not be allowed to pitch except in the following scenarios:
• They are designated as a "Two-Way Player." A player can only qualify for this designation if he accrues at least 20 Major League innings pitched and at least 20 Major League games started as a position player or designated hitter (with at least three plate appearances in each of those games) in the current or prior season.
• A game goes into extra innings.
• A player's team is losing or winning by more than six runs when he enters as a pitcher.