Arizona Fall League Will Feature Several Experimental Rule Changes In 2021

Image credit: (Photo by Bill Mitchell)

Pitch clocks, shift restrictions and more changes are coming to the Arizona Fall League.

Major League Baseball officials confirmed to Baseball America on Thursday that the AFL will feature most of the experimental rules changes that were introduced in the minor leagues this year.

Pitchers will be subject to a 15-second pitch clock and limited to two pickoff attempts per plate appearance, infielders will be required to remain in the dirt with two positioned on each side of second base and the size of the bases will be increased.

The automated ball-strike system, which the AFL experimented with in 2019, will be used in games played at Salt River Fields.

“We will have a lot of the greatest hits making their way to the Fall League,” MLB executive vice president of baseball operations Morgan Sword said.

MLB introduced each rule in different leagues and levels of the minors in 2021. Pitch clocks were put in place in the Low-A West, the automated ball-strike system was used in the Low-A Southeast, pickoff limitations were enforced throughout Low-A, shift restrictions were introduced at Double-A and larger bases were used at Triple-A.

The AFL presents an opportunity to see what games look like with all of the rule changes in place simultaneously. MLB plans to collect data from the AFL and add it to the data it collected during the regular minor league season. The full data set from the regular season and the AFL will be used to determine which rules changes league officials recommend be kept for future seasons.

“We plan to discuss with the competition committee this offseason the results of each rules experiment and what if anything we’d like to do going forward with that rule,” Sword said. “We’re currently working through all the data and interviewing a lot of players and coaches and doing everything we can to provide a comprehensive report to the competition on how this year went. That will be a project for the next couple months, to start thinking about which of these rules should be advanced or used in a broader way, which should be adjusted (and) which should be dropped entirely.”

The effect of each rule change during the 2021 minor league season varied. The 15-second pitch clock and pickoff limitations led to significant changes in outcomes, while larger bases had a minor effect and shift restrictions had almost no effect.



The 15-second pitch clock was introduced in the Low-A West on June 8, five weeks into the season, and average game times shortened significantly after it was put in place.  

Nine-inning games prior to the introduction of the pitch clock lasted an average of 3 hours, 2 minutes, while nine-inning games after the introduction of the pitch clock averaged 2:41. The introduction of the pitch clock also corresponded with an increase in offense throughout the league.

“The pitch timer was one of the more successful experiments from this season,” Sword said. “We received very positive feedback on the timer from players, coaches umpires, minor league operators, frankly everybody that was involved in the Low-A West league this year. We were very encouraged by how it went.”

The limit of two pickoff attempts per plate appearance was also introduced in Low-A this season and led to an increase in both the number of stolen base attempts and the success rate on stolen bases. The number of stolen base attempts at the level rose from 2.4 per game in 2019 to 3.2 per game this year with the limit in place. The success rate rose from 68% to 77%.

There were two different rules governing the positioning of infielders in an attempt to limit shifting at Double-A this year. All four infielders were required to remain in the dirt for the first half of the season and two infielders were required to remain on either side of second base during the second half. The AFL will use the second-half rule.

Both versions of the shift restriction resulted in no significant change in batted-ball outcomes at Double-A. Nonetheless, MLB will apply the second-half rule to the AFL to gather additional data.

The size of the bases increased from 15 inches square to 18 inches square at Triple-A for half of the season in each of the two Triple-A leagues. The change led to a slight increase in the success rate on stolen base attempts and led to a decrease in the number of collisions and injuries sustained around the bag, according to Sword, although specific data was not available.

The AFL begins play Oct. 13 with the new rules in place.

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