Baseball replay can correct certain missed calls, but it does not let a team challenge every judgment an umpire makes. The key is whether the play is reviewable, whether the manager still has a challenge, and whether the video shows enough to change the ruling on the field.
Replay review is a procedure for checking specific calls with video. It is not a full appeal of the inning, and it does not replace the umpire's live judgment on every part of the play.
In MLB, replay officials at the Replay Command Center make the final decision. They can confirm the call, change the call, or let the call stand when the available video does not provide clear enough evidence to overturn it.
A manager challenge is the normal way a team asks for replay during much of the game. In regular MLB games, each club starts with one manager challenge. All-Star and postseason games start with two. If any challenged call within the play is overturned, the club keeps its challenge. If no challenged call is overturned, the club loses that challenge.
The manager must first signal that the team is considering a challenge. In MLB, that starts a 15-second timer for the manager to decide whether to challenge. The manager also has to identify the specific call being challenged. Replay officials do not use a manager challenge as permission to search the whole play for unrelated missed calls.
The crew chief can initiate a review of a potential home run call at any time. Beginning in the eighth inning of an MLB game, the crew chief also has broader authority to review calls that are otherwise reviewable, including when a manager has no challenges left.
This does not make every late-game argument reviewable. The same basic limit still applies: the issue must be one the replay rules allow officials to review.
Many baseball arguments are not standard replay issues. Balls and strikes, most check swings, balk judgments, infield fly judgments, and ordinary safe-or-out calls that are not within the review rules cannot simply be reopened because the dugout dislikes the call.
Some plays have reviewable and non-reviewable parts. For example, replay may decide whether a pitch touched the batter, clothing, or bat, but not whether the pitch was in the strike zone or whether the batter made enough effort to avoid it. The review is limited to the facts the rulebook permits.
Replay is not decided from scratch. The ruling made on the field remains the starting point. If the video clearly shows the call was wrong, the replay official can overturn it. If the video supports the call, it can be confirmed. If the video is inconclusive, the call stands.
That is why two similar plays can produce different replay results. The question is not whether the play looked close on television; it is whether the available angles are strong enough to change the original ruling.
When a call is overturned, replay officials and the umpiring crew must put the teams as close as possible to where they would have been if the correct call had been made live. That can mean changing an out, awarding or removing a run, placing runners, correcting possession of a base, or resetting the count, score, and game situation connected to the reviewed play.
Once replay review begins, players and managers cannot keep arguing the reviewed call or the replay decision. In MLB, further argument after review can lead to ejection, and the replay official's judgment decision is final.
A runner is called out trying to steal second. The manager can challenge whether the tag beat the runner to the base. Replay can check the tag and the runner's touch of second. It normally will not turn that same challenge into a review of an earlier pitch location, a possible balk, or an unrelated obstruction argument unless the replay rules specifically allow that issue to be reviewed.
If the video clearly shows the runner touched second before the tag, the call can be overturned. If the angle is blocked, the call may stand even if fans think the runner was probably safe.