Major League Baseball will implement a handful of rule changes at various levels of the minor leagues during the 2026 season. Eric Longenhagen of FanGraphs first reported the slate and those interested in the topic are encouraged to read that post in full.
The most notable is the introduction of the check-swing challenge system in the Triple-A Pacific Coast League, beginning in early May. That allows a batter, pitcher, or catcher to challenge an umpire’s check-swing decision against bat-tracking technology. MLB had tested this rule in the Low-A Florida State League and the Arizona Fall League last year.
A check-swing challenge system requires an objective cutoff point. The threshold is whether the bat head breaks a 45° angle relative to the handle (essentially aligning with the opposite base line). Major League Baseball’s rulebook doesn’t have an official check-swing cutoff, instead leaving it at the umpire’s discretion as to whether the hitter offered.
As Longenhagen demonstrates with video, the 45° threshold is further along than what umpires have generally treated as the cutoff. That led hitters to successfully challenge a lot of calls last year. It appears that’s a deliberate consideration by the league. MLB’s memo notes a slight drop in the Florida State League strikeout rate after the check-swing challenge was implemented, “having a positive impact on balls in play and encouraging more extensive testing at higher levels.” It’s not a huge effect but one that would turn more swinging strikes into balls than vice versa.
The check-swing challenge will only be tested in the Pacific Coast League. In the other half of Triple-A, the International League, MLB will instruct umpires to visually use the 45° degree cutoff but will not give players the right to challenge. That’s seemingly to set up some kind of control group vs. the PCL while encouraging umpires to be more forgiving on check-swing calls generally.
Additionally, there’ll be a slight adjustment to the positioning of the second base bag in the International League. That change, which goes into effect in the second half of the 2026 season, moves the bag a little closer to the pitcher’s mound and reduces the distance from second to the corner bases by roughly nine inches in both directions. As with the previously implemented change to enlarge the bases, it’s designed to encourage more aggressive baserunning.
There are a few more minor tweaks related to pace of play and positioning of base coaches which the FanGraphs post covers in greater detail. There’s also the introduction of a reentry rule for a pulled starting pitcher at the rookie ball levels. Unlike the other rule changes mentioned here, that is not being tested for eventual implementation in MLB. That’s simply designed to avoid overworking young pitchers — most rookie ball players are teenagers — who are struggling to throw strikes, hopefully reducing injury risk.
MLB tests a number of rule adjustments in the minor leagues or independent ball. Some of them like the pitch clock, the ball-strike challenge system, and shift limitations make it to the highest level. Others (e.g. the DH “double-hook,” designated pinch-runners) have not.
The check-swing rule seems to be the one worth most closely following of this year’s group. “We haven’t made a decision about the check-swing thing,” commissioner Rob Manfred told Evan Drellich of The Athletic last June. “We do try to think sequentially about what’s coming. I think we got to get over the hump in terms of either doing (ball-strike challenges) or not doing it before you’d get into the complication of a separate kind of challenge involved in an at-bat, right? You think about them, they’re two different systems operating at the same time. We really got to think that one through.”
