15-day Injured List
The 15-day injured list is specifically for pitchers and two-way players. It allows clubs to remove injured pitchers and two-way players from the 26-man active roster while keeping them on the 40-man roster.
Players on the 15-day injured list must remain out of action for at least 15 days, though a player can also stay on the list for considerably longer than 15 days, if necessary.
Players may be placed on the 15-day injured list "retroactively," meaning the stint is backdated to the day after the last date on which the player appeared in a game. The maximum an IL stint can be backdated is three days, even if a player hasn't appeared in a game for longer than that. For instance, if a player last played on June 1 but isn't placed on the 10-day IL until June 7, the player's team can backdate the 10-day IL stint to June 4. He would be eligible to return from the IL on June 19.
As part of the 2017-21 Collective Bargaining Agreement, the 10-day injured list replaced the 15-day injured list as the shortest option for non-concussion injuries. Baseball had a 10-day injured list at various points through its history before it was dropped in 1984.
MLB brought back the 15-day IL for pitchers and two-way players in 2022, with the 10-day IL remaining in place for position players.
MLB teams must designate every player on the active roster as either a pitcher or a position player and are limited to carrying 13 pitchers on the active roster (14 pitchers from Sept. 1 through the end of the regular season). Those designated as position players are unable to pitch unless it is extra innings or their team is ahead or trailing by more than six runs when they take the mound. Teams can also designate players as two-way players if they meet certain criteria. Two-way players are able to pitch in any situation but don't count toward the active roster's pitcher total.