The 10-day disabled list -- or "DL" -- allows clubs to remove players from the 25-man active roster while keeping them on the 40-man roster. Players can be placed on the 10-day DL for any type of injury, though players with concussion symptoms are first sent to the 7-day DL. Players on the 10-day DL must remain out of action for at least 10 days, though a player can also stay on the list for considerably longer than 10 days, if necessary.
Players may be placed on the 10-day DL "retroactively," meaning the DL stint is backdated to the day after the last date on which the player appeared in a game. For instance, if a pitcher is diagnosed with elbow inflammation on June 4 after feeling soreness during his June 1 start, he could be placed on the 10-day DL on June 4 retroactive to June 2. In that case, he would be eligible to return from the disabled list on June 12.
History of the rule
As part of the 2017-21 Collective Bargaining Agreement, the 10-day DL replaced the 15-day DL as the shortest DL option for non-concussion injuries. Clubs have three disabled-list options: The 7-day DL (solely for players experiencing concussion symptoms), the 10-day DL and the 60-day DL. Baseball had a 10-day disabled list at various points through its history before it was dropped in 1984.
Nationals shortstop Trea Turner suffered a right hamstring strain during a game on April 8, 2017, and was placed on the 10-day DL on April 10, retroactive to April 9. He was activated April 21.