Major League Baseball made its rule changes for the 2020 season official on Wednesday.

There are four categories of rules going into effect: the three-batter minimum for pitchers, roster limits, adjustments to the injured list and option periods for pitchers and two-way players, and a reduction in the time managers have to challenge a play. All but one of these changes -- the one addressing manager challenges -- had been publicly reported prior to Wednesday, but now they are all locked in.

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All pitchers -- both starters and relievers -- now have to face at least three batters (or pitch until the inning is over) before they come out of a game. The only exception is an injury or illness that prevents the pitcher from being able to finish his three batters.

The main effect of this rule will be on specialist relievers, who are often used for only one batter to give their team a favorable matchup -- for example, a left-handed pitcher who faces only left-handed hitters, whom he is most likely to get out (often nicknamed a “LOOGY,” for “left-handed one-out guy”). There will be no more of that in 2020. The rule could also impact teams that use openers -- typical relievers who start a game to match up specifically against the top of the opposing order. Now, an opener would have to face at least three batters even if he has a bad matchup in that run.