Did Pitch Clocks, Robo Umps And Other 2021 MiLB Rules Changes Work?

Image credit: (Photo by Carl. D Walsh/Portland Press Herald)

At a Low-A game between Rancho Cucamonga and San Jose in August, three high-ranking Major League Baseball officials sat in the stands and watched the league’s experimental playing rules unfold in real time.

Senior VP of minor league operations Peter Woodfork and senior VPs of on-field operations Michael Hill and Raul Ibañez sat about a dozen rows behind home plate and watched Rancho Cucamonga and San Jose complete a nine-inning game in 2 hours, 28 minutes. The night before, they saw Lake Elsinore and Inland Empire finish a game in 2:24. Both games were played with a 15-second pitch clock, which was implemented in Low-A West earlier in the season.

After the final out in Rancho Cucamonga, all three officials couldn’t help but remark at the pace of play with the pitch clock in place.

Their enthusiasm is widely shared by MLB officials in New York.

“The pitch timer was one of the more successful experiments from this season,” MLB executive vice president of baseball operations Morgan 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.”

MLB enacted six experimental rules changes in the affiliated minor leagues this season, staggering them at different levels to see how they played out in isolation. Now that the 2021 minor league season has largely concluded, officials are reviewing the effects of the rules changes on each league to determine if they should be kept—or expanded—moving forward.

First and foremost is the pitch clock. The 15-second timer was introduced into Low-A West on June 8, five weeks into the season, and led to a decrease of 21 minutes in the average time of a nine-inning game, as The Athletic’s Jayson Stark first reported.

Games from Opening Day through June 7, prior to the implementation of the pitch clock, averaged 3:02. Games from June 8 through the end of the regular season, with the pitch clock enforced, averaged 2:41. As Stark also first reported, the introduction of the pitch clock also corresponded with an increase in batting average, runs and home runs and a decrease in walks and strikeouts.

w/o pitch clock 5.13 .237 .333 .371 1.9 11.1 29.3
w/ pitch clock 5.86 .263 .347 .424 2.5 9.7 25.3

Source: MLB Research

“I thought it was really good,” said Inland Empire manager Jack Howell, who played 11 seasons in the major leagues. “I thought it really helped. It just kept the pace, the flow of the game going better. And it was better for our pitchers, teaching them to work quick. Get your sign and go.”

While there were other elements in play, the pitch clock was the overriding factor in the reduction of the league’s average game time.

Another experimental rule designed to increase the pace of play limited pitchers to two pickoff attempts per plate appearance in all Low-A leagues. The rule made no significant difference in the game times in Low-A West.

Nine-inning games in the league (when it was known as the California League) lasted an average of 3:03 in 2019, with no limits on the number of pickoff attempts. Games this year lasted the aforementioned 3:02, a decrease of only 1 minute, when the pickoff limit was in place but the pitch clock was not.

This was not the minors’ first experience with a pitch clock, but it was its most effective.

Since 2018, pitchers at Double-A and Triple-A have had a 15-second pitch clock with no one on base and a 20-second pitch clock with runners on.

Despite those restrictions, the length of games has increased at both levels.  The average time of a nine-inning game at Double-A rose from 2:43 in 2017 to 2:55 in 2021. The average time of a Triple-A game rose from 2:55 to 3:04.

There were two fundamental differences that made the Low-A West pitch clock more effective at reducing average game times. The first is there was less time on the clock. The pitch clock rose to 17 seconds with runners on base in Low-A West, compared to 20 seconds at higher levels. Batters were also required to be in the box ready to hit with eight seconds remaining on the clock, compared to seven seconds at higher levels.

The second, and more significant, difference was how the pitch clock was enforced. Pitchers at Double-A and Triple-A can step off the mound and have the pitch clock reset with no penalty. In Low-A West, stepping off the mound counted as one of the pitcher’s pickoff attempts. He could step off twice and have the clock reset, but the third time he’d be called for a balk.

“We removed a lot of the quote-unquote loopholes that existed in the Triple-A and Double-A pitch clock,” Sword said. “I think that’s why we saw such a better result in Low-A West compared to some other levels.”

The 15-second pitch clock will be used in the Arizona Fall League this year, but no additional commitment has been made beyond then. MLB is still gathering information and feedback on all of the rules changes and has not yet made an official decision on which rules will be kept or expanded in 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 committee 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.”

In addition to the pitch clock, here is an overview of the rest of the experimental rules changes that were implemented in the minor leagues for the 2021 season. This includes the results of those rules changes and what support exists for keeping them moving forward.




MLB increased the size of the bases at Triple-A from 15 square inches to 18 square inches for half of the season in each league. The larger bases were used in Triple-A East for the first half of the season and in Triple-A West for the second half of the season. The goals of the change were to increase the success rate on stolen base attempts (larger bases equals a shorter distance between them), increase the number of infield hits and decrease the number of collisions around the bag.

The larger bases did result in higher stolen base success rates. Runners were successful on 76% of stolen base attempts at the Triple-A levels this season through Sunday. The success rates ranged between 69-72% each season from 2015-19.

“Not in a dramatic way, but it did kind of move the numbers in the right direction,” Sword said. “The other positive was the adjustment period it required of players was very short. Some players reported they barely even noticed the larger bases. And it had some pretty significant health and safety benefits, too, in terms of the number of injuries that occur on and around a base. That one, we also had a pretty positive takeaway.”

Farm directors and Triple-A managers echoed the sentiment that the change caused little noticeable disruption.

“There was nothing that stood out to me that was like ‘Wow, that really changed the game,’ ” Round Rock manager Kenny Holmberg said. “It wasn’t anything good, it wasn’t anything bad. It was just kind of indifferent. The bases just were bigger.”

The exact number of how many additional infield hits or fewer collisions occurred with the larger bases is not available. Still, Sword said he agreed with the characterization that larger bases and the pitch clock were the two most successful rules changes enacted in 2021.

“I think so,” he said. “If by successful you mean had the desired effect with sort of minimal disruption, yeah. I think that’s probably right.”


MLB introduced a pair of rules limiting shifting at Double-A. In the first half of the season, all four infielders were required to have both feet in the dirt when the pitch was delivered. In the second half, two infielders were required to be on each side of second base in addition to being in the dirt.

The thought was by limiting shifts, more balls in play would get through the infield for hits. After compiling data throughout the year, however, MLB found no significant difference in batted-ball outcomes by limiting shifts.

The batting average on balls in play at all Double-A leagues was .309 in 2018 and .305 in 2019. In 2021, with shift restrictions in place, the batting average on balls in play was .307.

“I wouldn’t say that there was anything in the data so to suggest a dramatic effect of the shift restrictions,” Sword said. “We kind of rigged it up by righties and lefties, who are affected a little bit differently by shifting, and in terms of how hard the balls are hit. There’s slight differences, but generally there was not a large effect of those restrictions being in place.”

2018 .309 8.34
2019 .305 7.90
2021 first half .307 7.86
2021 second half .308 8.09
2021 overall .307 7.97

Sources: MLB Research, Baseball-Reference

Double-A managers’ experiences largely matched with those findings. Many noted that while some balls that would have been outs with the shift turned into hits, other balls that would have been hits against the shift turned into outs with infielders playing straight up.

“I didn’t see any advantages or disadvantages to it at all,” Pensacola manager Kevin Randel said. “In the end it all kind of evened out. You steal some outs and you give up some cheap hits. I think it was pretty much all the same.”

“I’m kind of impartial to be honest with you,” Mississippi manager Dan Meyer added. “The rule helped us at times and a few times it hurt us … As far as any strong feelings, to be honest with you, I don’t really have any.”

With no significant difference in batted ball outcomes by limiting the shift, such restrictions could be unnecessary moving forward. However, Sword noted shifting is less prevalent in the minors, and thus the restrictions may not have been as impactful as they would be in the majors.

MLB implemented the second-half shift restrictions in the Arizona Fall League and will continue to gather additional data.


MLB required pitchers at High-A to fully step off the rubber before attempting a pickoff throw this season. The rule eliminated the Andy Pettitte-style pickoff move where a lefthanded pitcher could hang on his back leg in his delivery before deciding whether to throw home or attempt a pickoff at first base.

MLB experimented with the rule in 2019 in the independent Atlantic League and was originally set to implement it for the 2020 minor league season before the season was canceled due to the coronavirus pandemic.

As happened in the Atlantic League, the step off rule led to an increase in the number of stolen base attempts and stolen base success rates. From 2015-19, teams averaged 2.4 stolen base attempts per game in High-A. In 2021, they averaged just under 2.85 attempts per game. The success rate on stolen bases rose from nearly 68% from 2015-19 to just under 76% this season.

Year SB Att Pct. Att/G
2015 3569 5220 68.4 2.51
2016 3491 5113 68.3 2.47
2017 3342 4958 67.4 2.41
2018 3112 4628 67.2 2.25
2019 3255 4845 67.2 2.37
2021 3821 5040 75.8 2.84

While there were concerns about stolen bases becoming too easy or too prevalent with the rule change, the result was less than one additional stolen base attempt every other game.


“It’s hard to know exactly what the right number of stolen base attempts is, but … that doesn’t feel dramatic to me,” Sword said. “You probably wouldn’t even notice it, but I know that we did have some people react strongly to that. Particularly, lefthanded pitchers feel like they were constrained in their ability to hold runners.”

There was one unintended consequence of the rule. Double-A managers noted that when pitchers were promoted to the level from High-A, they often struggled to re-learn their former pickoff moves.

“The guys that came up, it took them a while to get adjusted back to picking like normal,” Randel said. “We had some lefties that lost their moves a little bit and some righthanders lost a little foot quickness. Some got it back, but some still looked awkward.”


MLB experimented with a different rule to encourage stolen bases in Low-A, limiting pitchers to two pickoff attempts per plate appearance. A third pickoff attempt, if unsuccessful, resulted in a balk.

Teams averaged 2.4 stolen base attempts per game in Low-A in 2018-19. With the new limit in place, they averaged nearly 3.2 steal attempts per game this season. The success rate rose from 68% to 77%.

Year SB ATT Pct. Att/G
2018 3359 4978 67.5 2.42
2019 3461 5072 68.2 2.44
2021 4357 5656 77.0 3.18

“You’re approaching one extra stolen base attempt per game, that’s a positive,” Sword said. “Nothing really to indicate that it was out of control or crazy in any way.”

The pickoff limit was tied in with the pitch clock in Low-A West. If a pitcher stepped off the mound to reset the clock, it counted as one of their pickoff attempts. As such, the rule had an effect on both the pace of play and increasing the number of stolen bases.

In the opinion of Low-A West managers, that wasn’t a bad thing.

“I think it helped with pitchers having a better tempo,” Howell said. “And then when they do go to the plate, be quicker to the plate. I was a fan.”


MLB instituted the automated ball-strike system, colloquially known as “robo-umps” in the Low-A Southeast this year, with balls and strikes determined by the Hawk-Eye tracking system and relayed to the home plate umpire via an earpiece.

One problem that quickly arose was young pitchers at the lowest levels of the minors lacked the control to consistently throw strikes, and umpires were unable to adjust the strike zone to help speed games along as they normally would. With an increase in walks lengthening game times, MLB adjusted the strike zone beginning July 26. They eliminated 3 ½ inches off the top of the zone, widened it by two inches on each side of the plate and changed where pitches were registered from the front of the plate to the middle of the plate.

The changes correlated with slight increases in batting average and slugging percentage and a reduction in walks and strikeouts. League batters hit .234/.346/.367 with a 12.9% walk rate and 26.8% strikeout rate through July 25. They hit .238/.339/.376 with an 11.4% walk rate and 26% strikeout rate after July 26, when the zone was altered.

Pre-altered zone .234 .346 .367 2.0 12.9 26.8
Post-altered zone .238 .339 .376 2.1 11.4 26.0

“We sort of separate the ABS test into two different issues,” Sword said. “The first is the technology. Just making sure that we can successfully track the pitch, produce the correct call and get it to the umpire’s ear as quickly as possible. On the technology side, it was extremely successful. We feel the technology is very good and this was our first full season running it on the Hawk-Eye tracking system.

“The second question, which is difficult, is what strike zone do you want to load into the ABS system? We started out with the rulebook system and then we switched during the season to what we’re calling, quote-unquote, the optimal zone, which is a little bit wider and a little bit shorter. Switching to the optimal zone did have the impact we were hoping.”

Even with the change, however, league managers noted there were still flaws in the ABS and how pitches were called.

“I thought the zone at the beginning of the year was a little bit tall … and then in the second half I thought it was too east-west,” Fort Myers manager Brian Meyer said. “They wanted it called a strike for like a ball(‘s width) off, but then you get a ball that clips and all the sudden that ball is four inches outside as opposed to just two.”

In addition to the kinks still to be worked out, the change to an “optimal zone” creates an element of subjectivity to the strike zone. The size of the called strike zone generally shrinks at higher levels, so the “optimal zone” at one level would not be the optimal zone in another.

“I don’t think we are confident yet that we know how that optimal zone would look at a higher-level league, like Triple-A for example,” Sword said. “But at least at Low-A it did move things in the right direction.”

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