What Minor League Rule Experiments Taught MLB

By 4Baseball Staff · November 5, 2026 · 10 min read

How the pitch clock, bigger bases, pickoff limits and shift rules were tested in the minor leagues before 2023, what the major-league numbers showed afterward, and what no experiment could predict.

When the major leagues introduced a pitch clock, larger bases and limits on pickoff throws in 2023, the changes looked sudden to fans who watched only the big-league game. They were not. Most of them had spent years in minor-league parks, where the rules were changed on purpose, season after season, to see what would happen. The pitch clock in particular had been running in the upper minors since 2015.

This article follows those experiments from the minors to the majors. It explains what each rule was meant to do, what the minors could and could not show, and what the major-league numbers say about the result. It uses historical data through the 2025 season for the league-wide totals, and it is careful to say where the data stop being able to answer the question.

Why the minors are the laboratory

A rule change in the majors needs the agreement of owners and players, and for decades the union and the commissioner's office could block each other's ideas. The minor leagues are different. Their players are not covered by the major-league collective bargaining agreement, the clubs are tied by affiliation agreements to major-league organizations, and the schedule is built around development as much as winning. A rule can be imposed in a league of one level and a handful of ballparks with little of the negotiation a major-league change would require.

The structure of that relationship changed after the 2020 season. Major League Baseball took direct control of the affiliated minor leagues, reduced the number of affiliated clubs and replaced the old player development contracts with new licenses, a transformation covered in minor league affiliation explained. One result was that MLB could run the same test in every park of a league without the usual local negotiation. It also gave the league data on a scale that a handful of independent-league tests could not.

The independent Atlantic League played a separate role. It had no affiliation with the majors, and MLB used a partnership with it to try ideas that were more extreme than anything it would test with its own prospects. The experiments that came out of that arrangement included automated ball-and-strike calling and a pitching rubber moved back by a foot.

The timeline in brief

The dates and details come from the public record of the experiments, and a reader who needs the exact timer lengths at each level should check MLB's announcements. The pattern matters more than any single date: the major leagues rarely adopted a rule on its first test. The pitch clock was tried in various forms from 2015 until it reached the majors in 2023, and it changed in length from level to level and year to year.

The pitch clock

The idea is simple. A pitcher has a fixed number of seconds to begin his delivery, and a hitter has to be in the batter's box and ready by a set time before the clock expires. If the pitcher is late, the umpire calls a ball. If the hitter is late, he is charged a strike. In the 2023 major-league version the timer ran 15 seconds with the bases empty and 20 with runners on, the batter had to be set with eight seconds remaining, and in 2024 the runners-on limit was reduced to 18 seconds.

The motive was pace. Games had lengthened over many years, not because the action grew but because of the time between pitches, with batters stepping out and pitchers pacing through long preparations. The rule makes the time between pitches a number of seconds and not a convention. The top levels of the minors showed that a clock could shorten games without changing the rest of the game, and they also showed how to enforce it: with an umpire's countdown at first and a visible clock in the stadium.

What the minors could not test was the full major-league environment. The fatigue of a 162-game season on a pitcher working to a clock, the ability of elite hitters to work around it and the difference in timing between prospects and veterans all appeared only once the rule reached the highest level. Concerns about whether a faster pace increases the risk of arm injuries were raised by players and trainers, and the data used here cannot settle the question. The development side of that concern is covered in how teams develop pitchers in the minors.

A worked example: what a few seconds adds up to

The size of the pitch clock's effect is easy to underestimate because each saving is tiny. Suppose, purely as an illustration, that a game contains about 290 pitches and that the clock trims an average of five seconds from the gap before each one. Five seconds multiplied by 290 pitches is 1,450 seconds, or a little over 24 minutes. The real figure depends on the actual pitch count and on how long the gaps were to begin with, which the historical record does not record, but the arithmetic shows why a rule that touches only a few seconds at a time can change the length of a game by a visible amount.

The same arithmetic explains why the limit on pickoff throws mattered. A throw over to first base costs a few seconds, and a pitcher who makes several in one at-bat adds a full minute of nothing to the game. Limiting the throws removed that time and, as the steal totals show, changed what runners were willing to try.

Pickoffs, bigger bases and the return of the steal

The second set of experiments aimed at the stolen base. The number of steals had fallen for years, and the cause was arithmetic: a runner needs to succeed roughly three times in four to make an attempt worth the risk, and with pitchers making repeated pickoff throws and catchers throwing well, teams stopped trying. The minor-league tests limited the number of times a pitcher could step off the rubber or throw over to a base, and made the bases bigger.

In the majors, a pitcher in 2023 could disengage from the rubber, by a pickoff throw or step-off, twice per plate appearance. A third disengagement had to result in an out, or the runner advanced a base on a balk. The bases themselves grew from 15 inches square to 18 inches, which also shortened the distance between them by a few inches. The reasoning was partly safety, since a larger base gives more room at first base, and partly to make a steal slightly easier.

The historical data show what followed. The table compares the last seasons before the change with the seasons since. SB and CS are stolen bases and times caught stealing for both leagues combined, and the last two columns show the rate per team game.

The jump from 2022 to 2023 is large: stolen bases rose by 1,017, about 41 percent, and the success rate climbed nearly five points to 80.2 percent. The count has stayed above 3,400 in each season since. That is the clearest effect in the whole experiment, and it matches what the minor-league tests suggested. The success rate has drifted down a little since 2023, which is consistent with defenses and pitchers adjusting, a pattern that the experiments could not predict because they ran only a season or two at each level.

The results also illustrate a basic point about experiments. The minor-league tests showed that limiting pickoffs made steals more successful. They could not show how teams would change their behavior once the whole league had the same rule. Major-league clubs responded by running more, and the baserunning data show that they did.

Shift restrictions and the batting average

The shift, in which fielders are positioned far from their traditional spots against a particular hitter, had reached the point where it was reducing the number of ground balls that became hits. The minor-league version required two infielders on each side of second base, with all four on the infield dirt when the pitch was delivered. The major leagues adopted the same standard in 2023.

The league-wide numbers are modest. Batting average for the American and National Leagues combined, computed from the historical batting file, was .243 in 2022 and .248 in 2023, then .243 in 2024 and .245 in 2025. A five-point rise in one season is consistent with the rule having helped hitters, but it is not large, and the next year it was gone. The league averaged 4.28 runs per team per game in 2022, 4.62 in 2023, 4.39 in 2024 and 4.45 in 2025. Several things changed at once in 2023, including the clock and the bases, so the historical data cannot separate the effect of one rule from another.

Strikeouts show something similar. The league averaged 8.40 strikeouts per team game in 2022, 8.61 in 2023, 8.48 in 2024 and 8.36 in 2025. The pitch clock did not produce a collapse in strikeouts or a surge in them, which is a useful result in itself. The long trend is covered in the evolution of the strikeout, and the hitting side of the development story is in how teams develop hitters in the minors.

Automated strike zones

The most ambitious experiment was an automated ball-and-strike system. Cameras and radar track each pitch, and a computer decides whether it crossed the strike zone. The Atlantic League tested the system in 2019, and it was later used in affiliated leagues. Two versions emerged. In the full system, the computer calls every pitch. In the challenge version, the human umpire calls pitches as usual, and a batter, pitcher or catcher can challenge a limited number of calls, with the computer deciding the result.

The experiments produced evidence on accuracy and also on timing and player behavior. Full automation raised questions about the definition of the zone, since a computer follows a three-dimensional shape and human umpires have long called a looser version. The challenge system kept the umpire's role and made the technology a check. Triple-A tested the challenge version alongside full automation from 2023, and the major leagues tested it in spring training in 2025. Through the 2025 season the regular-season rules were unchanged; MLB has since announced that the challenge system will be used in the major leagues for the 2026 season, and readers should check the current rulebook.

What the experiments could not teach

Minor-league experiments have limits that are worth stating. The players are younger and less polished, so a rule that works for prospects may behave differently with veterans. The sample is small: a few parks, a few seasons. The incentives differ, because minor-league players are trying to develop and be promoted, not to win games. And the minors cannot reproduce the postseason, the television schedule or the economics of the majors.

The experiments also changed as they went. The pitch clock was longer at some levels than at others, and the pickoff limits were adjusted. By the time a rule reached the majors it had been refined, and the version in the majors was not exactly the version that had been tested. That is a strength in practice and a weakness for anyone who wants a clean estimate of one rule's effect.

Some experiments did not move forward. The pitching rubber moved back a foot in the Atlantic League did not become a major-league rule. That outcome is a reminder that testing is also how a sport decides not to do something.

Common questions

Who decides on major-league rule changes? Under the collective bargaining agreement reached in 2022, a competition committee with six owner representatives, four players and one umpire can approve rule changes, and the league can also act on its own with notice to the union. Details are in the agreement and in MLB's announcements.

Did the pitch clock shorten games? Yes, by a substantial amount in 2023, according to MLB's reported averages; the historical record does not carry game times, so check the league's own figures.

Did bigger bases change anything? The largest visible change is in stolen bases, although the pickoff limits and the larger bases were introduced together, so the effect of each cannot be separated.

Is the automated strike zone in the majors? Through the 2025 season it had been tested in Triple-A and in spring training, and MLB has announced a challenge version for the 2026 season; check the league for the current status.

Where to go next

For the development side of the story, read how teams develop pitchers in the minors and the history of the amateur draft and signing bonuses. The league-wide numbers in this article can be explored on the leaders page and in the minors section, and the topic page for the minors is at minor league baseball. To read a box score from any of these games, see how to read a baseball box score.