The concussion list is a special form of injured list on which players are placed when they have or are suspected of having suffered a concussion. The list is meant to be more flexible than the regular injured list, because the effects of a concussion are normally of short duration (often, only a couple of days' rest are enough, but this cannot be predicted when the injury occurs). Before the list's creation, teams were sometimes reluctant to place a player on the DL with a concussion, as that made him unavailable for a minimum of two weeks. In turn, by remaining on the playing roster, there could be pressure for him to return to action before all of the effects of the concussion had dissipated, a very dangerous practice.
If the concussion is confirmed, there is a special medical protocol to be followed before a player can be reinstated, to ensure that he is not rushed back to action too soon. An independent physician appointed by Major League Baseball must confirm that the player is over the concussion before he is cleared to return.
The list was created in the early 2010s as a result of concern over the long-term effects of repeated concussions throughout professional sports. Players such as Mike Matheny and Brian Roberts had seen their careers shortened because of concussions. While such cases are rarer in baseball than in contact sports, concussions can result from being hit by a pitch or by a bat or a foul ball (in the case of catchers), or from accidental collisions on the basepaths or between fielders. The effects of concussion can be dramatic and are hard to detect by untrained persons, hence the need for special precautions.
In 2019, Pittsburgh Pirates GM Neal Huntington proposed a further refinement, allowing a player to leave a game to be tested for a concussion, and then to re-enter it if the tests prove negative. He argued that this would make players and teams more likely not to ignore possible concussions when immediate symptoms are not obvious, as they would not be penalized by losing a player for the remainder of the game if the concern proved to be a false alert.