The days of guessing why a reviewed call by an MLB umpire has been upheld or overturned appear to be coming to an end. According to ESPN's Pedro Gomez, MLB umpires will wear microphones during the 2020 season so they can announce to fans at the stadium and those watching or listening to the game why reviewed calls were upheld or overturned. Umpires can also make explanations if necessary, Gomez reports, and the process will be similar to the one used by NFL referees.
Consider this a welcome change that will help fans better understand the rationale behind replay review decisions. The difference between allowing a call to stand on the basis of insufficient video evidence and confirming a call will be of particular interest. Confirmed means that replay showed the original call to be correct, while allowed to stand in essence says we can't really tell and will default to the original call.
All replay reviews come from the replay command center, which is staffed by active MLB umpires on a rotating basis. Managers can challenge calls on the field, and in the event that a challenge results in an overturn, the manager retains his challenge. The umpiring crew chief can at any time call for a review of fair-foul calls on home run balls, and starting in the eighth inning the crew chief can initiate the review process of any reviewable call.
The replay process was expanded into the current format prior to the 2014 season. Since that point, observers have been left to speculate upon the precise reasoning behind a replay decision. Thankfully, some belated transparency appears to be in the offing, and the process figures to be improved as a result.