Challenge

Card game in Atlanta, an umpire called a 99-mph fastball a ball. Phillies catcher J.T. Realmuto tapped his helmet. Seconds later the call was reversed, strike three, and for the first time a postseason game had ended on a challenge.

That moment capped the rookie season of the Automated Ball-Strike Challenge System, the newest chapter in baseball's long argument over who judges the pitch. For the first time in the major leagues, a batter, pitcher, or catcher could dispute an umpire's call and...