Here are short thumb nails of each. Full descriptions with intended results are in an article posted on MLB by Anthony Castrovince.
- Triple-A: Larger bases. Slightly larger bases with a less-slippery surface. Base size increased from 15″ square to 18″ square. (It appears from Castrovince’s description that one expected result will be that the bases are a little closer, which makes sense. The distance between home plate and the corner bases will be shorter, too.)
- Double-A: Defensive Positioning. A minimum of four players on the infield. Four infielders must have their feet completely within the outer boundary of the infield dirt. Depending on first-half results, this may be modified to require two infielders on either side of second base.
- High-A: Step Off Rule. Pitchers must step completely off the rubber prior to throwing to any base. The snap throw by a left-handed pitcher followed by the step off is prohibited.
- Low-A: Pickoff Limitation, Pitch Timer, ABS. A limit of two step offs or pickoff attempts per plate appearance. On the third attempt, if the runner is not thrown out, the move is ruled a balk and any runners are automatically awarded the next base. Depending on the preliminary results of this change, MLB will consider further reducing the limitation to a single step off or pickoff per plate appearance.
- Low-A Southeast (Old Florida State League), ABS. An automatic ball-strike system will be implemented in selected Low-A Southeast games. The Hawk-Eye tracking system will be used to deliver an audio signal to the home-plate ump, who will then relay the ball or strike call.
- Low-A West: A 15-second pitch clock. A 15-second pitch clock was in use during the FSL’s 2019 season.
MLB will continue its three-year partnership with the Atlantic League. Any new experimental rules for the 2021 season will be announced in the coming weeks.