The new system, which will go into effect this season, will give managers most of the power to trigger reviews, by providing them with one challenge per game, along with a second potential challenge if their first is upheld.
Only after a manager has used up all of his challenges, and only from the seventh inning on, would umpires be authorized to initiate a review on their own.
For the first time, calls at first base, at the plate and on the bases will be reviewable. There will be limited exceptions, including the fabled "neighborhood play" at second base. But MLB executive Tony La Russa, one of the architects of the new system, estimated that almost 90 percent of all potential calls are now reviewable.
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