Introduced in the 2011 season, the 7-day disabled list was created specifically for players with concussion symptoms. Previously, the disabled list -- or "DL" -- had only two iterations: the 15-day DL and the 60-day DL. Major League Baseball instituted the shorter version of the DL to prevent a player with concussion symptoms from being rushed back before he is ready, while also allowing a player who passes concussion tests to return after only seven days rather than 15. The decision to change the 15-day DL to the 10-day DL -- as per the 2017-21 Collective Bargaining Agreement -- will not affect the parameters of the 7-day DL.
Players may be placed on the 7-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 player is diagnosed with a concussion on May 12 but last played on May 9, he could be placed on the 7-day DL on May 12 retroactive to May 10. In that case, he would be eligible to return from the disabled list on May 17. A 7-day DL stint cannot be backdated by more than five days.
The Tigers placed shortstop Jose Iglesias on the 7-day DL on April 21, 2017, retroactive to April 20, with a concussion. Iglesias was activated April 27, 2017 -- the first day he was eligible.
Note: The information contained in this glossary entry is subject to change as details emerge.