MLB test of robot umpires for checked swing calls moving up to Triple-A

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MIAMI (AP) — Major League Baseball's experiment of a robot umpire technology system allowing challenges to checked swing calls is moving up from Class A to Triple-A.

MLB will also test moving second base slightly to position it entirely within the infield, which would reduce by 9 inches the distance between first and second, and between second and third, according to a memorandum sent to teams last week.

It will try out reducing permissible disengagements by pitchers from two to one per plate appearance and stricter limits on batter timeouts and resetting the pitch clock for issues with PitchCom, the electronic signaling device that has been used since 2023.

There will also be a test allowing starting pitchers to re-enter games in the lowest level of the minor leagues. It's not expected this test will lead to MLB implementation, but it's being considered for the minors to improve development and player health by allowing more flexible workload management.

MLB's Automated Ball-Strike Challenge System, the so-called robot umpire, launches when the season starts March 25 following tests that started in the minors in 2019. A batter, catcher or pitcher can appeal a ball/strike call by the human umpire under a system in which each team has two challenges and keeps its challenge if successful. Additional challenges become available to teams in extra innings.

An experiment began last May 20 in the Class A Florida State League allowing challenges to checked swing calls, and the test was extended to the Arizona Fall League.

Starting on May 5, the checked swing test will take expand to the Triple-A Pacific Coast League in additional to the FSL.

“The batter, pitcher or catcher may also appeal the umpire’s decision regarding whether the batter swung at a pitch,” according to the memo from MLB vice president of on-field strategy Joe Martinez to general managers and other club executives. “A swing will be considered to have occurred if the maximum angle between the bat head and the bat handle exceeds 45 degrees.”

Martinez said the strikeout rate was cut by 3% during last year's testing.

In addition, umpires at games in the Triple-A International League will be instructed to apply the 45-degree threshold for determining swings starting May 5. The Official Baseball Rules do not specify a standard for checked swings, stating only: “A strike is a legal pitch when so called by the umpire, which is struck at by the batter and is missed.”

Since 1976, the rules have said: “The manager or the catcher may request the plate umpire to ask his partner for help on a half swing when the plate umpire calls the pitch a ball, but not when the pitch is called a strike.”

Starting pitchers will be allowed to re-enter a game after being removed at the Arizona Complex League, Florida Complex League and Dominican Summer League. A removed starting pitcher is eligible to return if he threw at least 25 pitches during the inning he was removed, can return only at the start of an inning and may re-enter only once.

MLB enlarged bases to 18-inch squares from 15 in 2023, a change the led to more stolen bases because of a decreased distance of 4 1/2 inches between first and second, and second and third.

Second base has been centered on the exact spot of second, but the experiment in the International League will place it “entirely within the perimeter of the infield diamond during the second half” of the season.

Citing an increase in the average time of a nine-inning game from 2 hours, 36 minutes in 2024 to 2:38 last year and a decrease in stole base attempt success rate from 80.2% in 2023 to 77.8% last year, MLB will experiment with changes to pitch clock rules.

Teams at Triple-A will be assessed a mound visit if play is stopped for a PitchCom problem, and if a team is out of visits an automatic ball will be charged.

At all levels, the clock will not stop when a catcher leaves the catcher's box to give defensive signals, and players other than the pitcher and coaches must leave the mound before the clock on mound visits runs out. A violation would result in an automatic ball.

At High A, batters will not be allowed to request time if the bases are empty and in Class A no timeouts will be allowed. Exceptions will be allowed for brush backs, possible injuries or equipment problems.

Allowed disengagements by pitchers from the rubber will be lowered from two to one at Double-A.

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