On the left, a replay of a hit-by-pitch play that is now under review. On the right, umpires await the call from MLB's review office. The play being reviewed involves a pitch to Ryan Jeffers of the Minnesota Twins, and the umpires include Laz Diaz on the left, and an unnamed replay review official on the right.
Replay Review
Most, but not all, plays that are called by umpires can potentially be subject to replay review. Replays are handled by a centralized office at MLB headquarters in New York city.
When a close play happens, the manager of the team on the wrong end of the play can immediately hold their hand out, signaling that they are thinking of asking for a challenge. The home plate umpire then starts a 15-second timer. Each team has a video review team posted somewhere in the stadium, who will review the play and make a recommendation as to whether or not a challenge would be reasonable1. If the manager decides to make the challenge, they usually do so via a signal (pantomiming putting a pair of headphones on). Managers can ask for multiple things to be reviewed in the same replay review.
At this point, the umpire crew chief does, in fact, put on headphones; usually, the umpire who made the call in question does so, as well. They are then put in touch with the replay review office. The replay office is also manned by umpires, who cycle in and out of said office along with their usual umpiring duties. The replay crew then reviews the play, using any and all video angles available to them— specifically, those provided by the TV crews for each game. Ideally, the replay crew will be able to reach a verdict within two minutes, after which they relay the results back to the umpires on the field. The crew chief then announces the call to the stadium.
When a review happens, there are three potential outcomes:
- Call is Confirmed: The replay umpires found that the call made on the field was correct; the call stands.
- Call is Upheld: The replay umpires were unable to find clear evidence to prove whether the call was correct or not. In the absence of such clarity, the original call on the field stands.
- Call is Overturned: The replay umpires determined that clear evidence exists that the original call was wrong. The call is reversed, and the umpires then have discretion to sort out any after effects (like the position of runners who may have been able to advance if the original call had been correct).
Whatever call comes back from the replay office is considered final; if an aggrieved manager argues the call afterwards, they will likely be ejected from the game.
Each team is given a replay challenge to use at the start of the game. When a manager uses a replay and is successful, the team retains their challenge. However, if they are unsuccessful, they lose their challenge, and can no longer challenge plays directly. Starting in the eighth inning, the crew chief can initiate a replay on their own volition (including at the prompting of a manager who has lost their challenges already). The crew chief can also ask for a replay of potential home runs that happen at any point in the game.