Umpires will now be equipped with on-field microphones to inform the crowd and television audience of instant replay reviews beginning with exhibition games at stadiums this weekend, Major League Baseball announced Friday.
Crew chiefs will wear a microphone, via a belt pack, and will proceed to one of the baselines when a replay is initiated and face the press box to make the announcement. They'll announce who is making the challenge, what is being challenged, and then -- after the review is completed -- announce the verdict and give a quick explanation.
https://www.espn.com/mlb/story/_/id/33645606/mlb-umpires-announce-replay-review-decisions-fans