MLB Announces New Minor League Rule Changes For 2021

Image credit: (Photo by Zach Lucy/Four Seam)

Major League Baseball on Thursday announced sweeping rules changes to be implemented in the minor leagues in 2021.

At Triple-A, the size of bases will increase from 15-by-15 inches to 18-by-18 inches. By doing so, MLB expects the slightly shorter distance between bases will lead to a higher success rate on stolen bases and more infield hits on grounders and bunts. 

At Double-A, efforts will be made to limit shifting and the ways teams can position their infielders. All teams must have at least four players on the infield during play, which is defined as having both feet “completely in front of the outer boundary of the infield dirt.” If the results of the rule change are deemed positive in the first half, the league may require teams to have at least two players on either side of second base in the second half. Essentially, these are gradual steps toward eliminating or reducing extreme shifts and making batters more successful on balls in play. 

High-A teams will implement a rule which was in play in 2019 in the Atlantic League. In these leagues, pitchers will be required to disengage the rubber completely before throwing to any base. With this rule in play, the Atlantic League saw a significant uptick in stolen bases. The rule was scheduled to be implemented in the minor leagues in 2020 before the coronavirus pandemic canceled the season.


Across Low-A, pitchers will be limited to two step-offs or pickoff attempts per plate appearance. If a pitcher tries a third pickoff in a plate appearance, the move will be considered a balk unless the runner is successfully picked off. Depending on the results of the rule change, MLB will consider reducing the number of pickoffs or step-offs per plate appearance to just one. 

At Low-A Southeast only, select games will use the automatic ball-strike system, which was tested in both the Atlantic League and Arizona Fall League in 2019. 

At Low-A West only, teams will add timers to enforce time between pitches, inning breaks and pitching changes. The release announcing the move noted “new regulations beyond the system currently used in Triple-A and Double-A.” 

The automatic ball-strike system was supposed to be implemented in the Florida State League in 2020, but that season was cancelled because of the coronavirus pandemic.

“These experimental rules are designed to put more balls in play, create more excitement on the basepaths and increase the impact of speed and athleticism on the field,” MLB senior vice president of on-field operations Raul Ibanez said in the release. “As another important goal of the rules approved by the Competition Committee and the Playing Rules Committee, we expect the new larger bases to increase player safety. We look forward to testing these rules in the Minor Leagues.”

The release also announced MLB would continue its partnership with the Atlantic League in order to test new rules for the future. Any rules changes for the Atlantic League will be announced later. The Atlantic League was supposed to move the mound back during the 2019 season, but that move was postponed and never implemented. It is not clear whether that move will return in 2021, but it was one that left some pitchers promising they would leave the league if it was implemented.


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