What the Minor League Data Says About New MLB Rules Changes

Major League Baseball is expected to adopt a trio of significant rules changes for the 2023 MLB season, with pitch clocks, a ban on infield shifts and larger bases all expected to come to the majors for next season. The news was first reported by The Athletic.

All three of these rules changes have been tested and trialed in the minor leagues over the last two seasons. That leads to the question, what have the minors shown about what these rules changes can mean in the majors.

The change that will likely be most noticeable to everyone will be the arrival of a pitch clock in the majors. There has been a pitch clock at the upper levels of the minors since 2015, but the version that was used from 2015-2021 was one with glaring loopholes. A pitcher could reset the clock simply by making a pickoff throw, for example. With that version, game times and pace of play sped up in 2015 with the average nine-inning game time of a Triple-A and Double-A game dropping by 11 minutes.

But those shorter game times and speedier pace of play quickly eroded. By 2021, Triple-A nine-inning games averaged 3:04 per game while Double-A games were taking 2:57 to play on average.

In 2022, the pitch clock rule adopted across the minors required batters to be in the batter’s box with nine seconds to go on the pitch clock. If they are not, an automatic strike is called. Pitchers are given 14 seconds to throw a pitch with no one on base and 18 seconds with a runner on base. (Triple-A’s times have been 15 seconds and 19 seconds, respectively). Pitchers are only allowed two pickoff attempts in any at-bat. If a pitcher throws over a third time and he does not pick off the runner, the runner is rewarded the next base automatically. A step off counts the same as a pickoff. Hitters are allowed to call time only once per at-bat as well.

With significantly fewer ways to reset the clock, the reduction on game time and the faster pace has been significant.

At Triple-A, the average nine-inning game in 2022 is taking 2:43, a reduction of just fewer than 21 minutes compared to 2021. At Double-A, the average game time has dropped by 17 minutes. At High-A, the average game is over 30 minutes shorter and Low-A game times have dropped by 24 minutes.

In Rookie ball, where there are no pitch clocks, the average nine-inning game has taken an additional minute, up from 3:12 in 2021 to 3:13 this year.

Those reductions have meant that average nine-inning game times have ranged from 2:34 (High-A) to 2:43 (Triple-A). In 2021, every level’s average nine-inning game took 2:57 or longer, with three of the four levels topping three hours.

Year	Level	Nine-inning Game Time
2022	MLB	3:04:24
*2022	Triple-A	2:43:23
*2022	Double-A	2:40:16
*2022	High-A	2:34:02
*2022	Low-A	2:36:34
2022	Rookie	3:13:26
2021	MLB	3:10:04
2021	Triple-A	3:04:11
2021	Double-A	2:57:40
2021	High-A	3:04:36
2021	Low-A	3:00:34
2021	Rookie	3:12:28
2019	MLB	3:05:32
2019	Triple-A	3:05:22
2019	Double-A	2:44:08
2019	High-A	2:51:37
2019	Low-A	2:53:17
2019	Rookie	3:04:44
*Uses new pitch clock rules

The reduction in pickoff throws as well as the advantages baserunners can glean from a clock ticking down (some runners will get an extra head start as the clock ticks to zero) have seen stolen bases skyrocket.

Across the minors, teams are averaging 1.4 stolen base attempts per game and 1.1 successful steals per game. The success rate across the minors is 77%. The 1.1 successful steals a game nearly matches the 1.11 stolen base attempts across the full-season minors in 2019.

The ban on shifts seems to be a significant rules change without nearly as much evidence that it will make a significant impact. The idea behind banning shifts is to lead to more base hits by reducing the ability to position fielders to take advantage of hitters’ tendencies.

But so far there has been little evidence that it leads to higher batting averages on balls in play (BABIP) in the minors. 

Those rules were adopted on an experimental basis in Double-A in 2021 with four infielders being required to have their feet on the dirt in the first half and an additional requirement to have two fielders on either side of second base in the second half. The batting average with balls in play with the restrictions was .308 overall in 2021, up from the .305 BABIP in Double-A in 2019, but down from the .309 BABIP in 2018.

This year, those shift rules were adopted across Low A, High A and Double-A, while Triple-A does not have shift restrictions. And if you look at the data without knowing which levels had added shift restrictions, you wouldn’t be able to easily tell which levels adopted shift restrictions and which did not.

In Triple-A, with no shift restrictions, the BABIP is up from .310 in 2021 to .311 in 2022. At Double-A, which has shift restrictions this year as it had last year, the BABIP is up three points to .311 from .308. In High-A the adoption of shift restrictions has seen the BABIP fall by seven points (.314 to .307). And in Low-A the BABIP has dipped from .323 last year to .317 this year.

Major League Baseball has added a further tweak to the shift rules in the Florida State League this year. In the second half of the season, the FSL is using a shift rule where no fielder can stand in a “pie slice” area extending behind second base. With the pie slice rule, hitters have a .307 BABIP in the second half of the season. They had a .313 BABIP in the first half with the infield shift rules that have been enacted across the minors.

The larger bases can best be described as a very minor tweak. Those 18-inch square larger bases were adopted across the minors in 2022 with little fanfare. The stolen base rate and success rate in the minors has skyrocketed in 2022, but that has much more to do with the other rules tweaks than it has with the larger bases.

Unlike this year, where they were adopted universally across the minors, larger bases were a split-season experiment in Triple-A in 2021. The larger bag at first makes it easier for first basemen to avoid being spiked, and there is some thought that the slightly larger bases (three inches larger than the previous 15-inch versions) would encourage base stealing.

In reality, the split-season experiment didn’t demonstrate that. In 2021, in the first half with smaller bases, Pacific Coast League teams stole .66 bases per game at a 75% success rate. In the second half of the season with the larger bases, they stole .61 bases per game at a 75% success rate. The International League saw steals go up from .76 stolen bases per game with the smaller bases to .83 bases with the larger bases, but the success rate dipped from 77% with smaller bases to 76% with larger bases.

The International League’s batting average with smaller bases in 2021 was .244, and with larger bases it was .245. The Pacific Coast League’s batting average in 2021 with smaller bases was .271 and was .270 with the larger bases. In other words, larger bases may reduce injuries due to collisions, but they are unlikely to change the offensive environment in any significant manner.

One item that didn’t make the list of 2023 MLB rules changes is the automated ball-strike system that has been experimented with at various levels of the minors and the partner-league Atlantic League for several years. While there have been plenty of mixed reviews about a fully automated strike zone, the experiment in 2022 where the home plate umpire calls balls and strikes, but each team has a limited number of appeals to check the call with the automated strike zone has generally received much more favorable reviews from players and coaches.