NEW YORK — Major League Baseball will implement its Automated Ball/Strike challenge system beginning with the 2026 season opener between the New York Yankees and San Francisco Giants. The system allows players to appeal ball and strike calls made by plate umpires throughout the game.

Each team receives two challenges per game at the start. Only the pitcher, catcher or batter may initiate a challenge by tapping his helmet or hat, and assistance from the dugout is not permitted when deciding to challenge a call.

When a player challenges a call, the umpire triggers a real-time replay of the pitch via animation shown publicly on displays. The challenged pitch appears as a graphic, after which the umpire announces the updated count.

Teams retain their ability to challenge after winning a challenge but lose the ability to challenge for the remainder of the game after two unsuccessful challenges. Teams that exhaust both challenges receive one additional challenge in each extra inning.

The system underwent testing before its major league debut. MLB tested it at the Triple-A level since 2022, during spring training last year, and at the 2025 All-Star Game in Atlanta. Video review systems were first introduced for home run calls in August 2008 and expanded to many calls for the 2014 season.

During 2026 spring training, 53 percent of 1,844 challenges proved successful. Defensive challenges succeeded 60 percent of the time, while batter-initiated challenges succeeded 45 percent of the time. Spring training games averaged 4.32 challenges per game, with an average of 2.28 successful challenges per game.

Stadiums employ a Hawk-Eye pose-tracking camera system to track each pitch and determine whether it crossed home plate within the strike zone. In early testing phases, umpires wore earbuds to hear "ball" or "strike" calls from the automated system and relayed those calls with hand signals.

Players must initiate challenges within two seconds of the pitch. Each player's height is measured without shoes between 10 a.m. and noon on a rolling basis during spring training to establish that player's strike zone. The system bases strike zone measurements on players' height rather than their batting stance.

Chicago Cubs hitters had a 65 percent success rate overturning calls in 2026 spring training. St. Louis Cardinals pitchers and catchers had a 75 percent success rate challenging calls, while Kansas City Royals hitters had a 31 percent success rate and Toronto Blue Jays pitchers and catchers had just over a 50 percent success rate.