Just over half the ball/strike challenges were successful on the first day of spring training games Friday as Major League Baseball prepared for the first regular-season use of the automated ball-strike system — the so-called robot umpires.

Thirteen of 23 calls were overturned during the five games, MLB said, which came to 56.5%.

There were an average of 4.6 challenges per game and 2.6 overturned calls per game.

Seven challenges were made of plate umpire Alex MacKay’s calls during Arizona’s 3-2 win over Colorado, and six were successful. The Diamondbacks had four of five decisions reversed and the Rockies were 2 for 2 in challenges.

MLB experimented with the ABS system during spring training last year and teams won 52.2% of their ball/strike challenges (617 of 1,182) challenges.

Each team has the ability to challenge two calls per game. Teams that waste their challenges get one additional challenge in each extra inning. A team retains its challenge if successful, similar to the regulations for big league teams with video reviews, which were first used for home run calls in August 2008 and widely expanded to many calls for the 2014 season.

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AP MLB: https://apnews.com/hub/MLB