Starting in the 2026 season, Major League Baseball players will be able to challenge called balls and strikes in regular and postseason games for the first time. If a call is overturned, the team retains that challenge; if a call is upheld, the team loses that challenge. Most MLB players have already experienced the ABS challenge system, whether in spring training this season or during their time in the minor leagues, where MLB has been testing ABS since 2021. Over four seasons of testing in Minor League Baseball, officials collected feedback from players, umpires and fans. MLB also tried out a "full ABS" system in which the system fed umpires the call of every pitch, but players and fans alike reported preferring the challenge system.