Getting a grip: After rubbing mud on baseballs for nearly a century, MLB experiments with a chemical substance

Wearing a turquoise button-down shirt with tropical print, umpire Clark Morgan stood in the concrete hallway leading to the visitor’s clubhouse at Ozinga Field in Crestwood, Illinois, gripping a baseball. Branded with a Frontier League stamp, the ball was smooth and unblemished, yet the familiar white of the leather was visibly tinted just slightly darker.

Behind the adjacent green door of the umpire’s room, Reid Hoover and Matthew Youkhanna, the other two members of that night’s crew, applied rubbing mud to several dozen other baseballs, depositing them in a white plastic bucket, in preparation for Saturday’s game between the visiting Washington Wild Things and the Windy City Thunderbolts.

This process of rubbing balls with mud, a specific kind known as “Lena Blackburne Original Baseball Rubbing Mud,” occurs throughout the United States baseball world. It’s done to give the balls, which come out of the box “very sleek and slippery” as Morgan puts it, a bit of tack (that is, stickiness to aid grip) for pitchers.

In the independent Frontier League, it’s the pregame responsibility of umpires. In the major leagues, clubhouse staff typically rub the baseballs. 

But Major League Baseball, through experiments in the minors, is exploring alternatives to the mud that’s been used for decades. This year, teams in the Class-AA Southern League used a baseball covered with a substance designed by the materials science company Dow for the first half of the 2023 season. 

A memo sent by MLB in March characterized the experimental balls as having an “enhanced grip.” In theory, it precludes both the need for rubbing mud and foreign substances that pitchers might use, against the rules, for increased performance.

Just like baseballs in the major leagues, the Dow balls are manufactured by Rawlings, according to Baseball America. The difference is the Dow substance applied to the ball (thus making the baseball “pre-tacked”) versus the usual rubbing mud.

“We continue to work with the people at Dow Chemical on developing a tacky ball,” MLB commissioner Rob Manfred said to the Baseball Writers’ Association of America in July. “It would literally eliminate all, well not all, but many of the variables in the current process. It would come out of a sealed foil pouch at the ballpark. No individual mudding.”

The substance on the experimental pre-tacked ball is proprietary, according to Dow spokesperson Kyle Bandlow.

“As a leading materials science company, Dow works closely with customers like Major League Baseball to tackle tough challenges and advance the game,” Bandlow wrote in an email. “However, Dow does not comment on pre-commercial innovations being conducted owing to the proprietary and confidential nature of such innovations.”

But statistical trends in the Southern League emerged that MLB almost certainly did not want to see. While Major League Baseball has recently changed rules (like banning defensive shifts, enforcing foreign substance checks on pitchers) to encourage more balls in play and action on the field, the Southern League saw a marked increase in overall strikeouts and walks and a decrease in batting average after introducing the new, stickier baseball. 

So, while professional leagues overseas, like Nippon Professional Baseball in Japan and the Korea Baseball Organization, use a pre-tacked ball that seems to mostly garner praise from players, Major League Baseball continues to struggle to find an alternative to rubbing mud.

Of the eight teams composing the Southern League, five declined to comment while three teams did not respond to multiple requests for comment. Neither Major League Baseball nor the Major League Baseball Players Association responded to requests for comment.

Erik Bremer, manager of broadcasting and media relations for the Pensacola Blue Wahoos, wrote in an email that “since this is a proprietary technology on MLB’s part they have recommended that our players and coaches not discuss the Southern League baseballs publicly.”

MLB and the Southern League experiment

The impact of the experimental baseball in the Southern League emerged quickly. 

A story from Sam Blum of The Athletic chronicled opening day for the Rocket City Trash Pandas, a Los Angeles Angels’ affiliate, in which 11 hitters came to bat before putting a ball in play.

By early May, Kyle Glaser of Baseball America identified statistical trends in the league (increased strikeouts, walks and wild pitches; decreased batting averages) that could largely be attributed to the new balls. Those developments continued up to the All-Star break in mid-July, the endpoint of the experiment. 

Worthy of note as well is that the Southern League used a baseball for two weeks last season covered in an unspecified gripping agent, according to a June 2022 report from Evan Drellich of The Athletic. That the league briefly used a tacked baseball last year too makes the statistical differences even starker when comparing the first halves of the 2022 and 2023 seasons.

On July 11, 2022, the combined rate of strikeouts per nine innings across the Southern League stood at 9.7. On July 13, 2023, that league-wide rate was 10.5, representing an eight percent increase between seasons. 

Batting average, meanwhile, declined about six percent between the first halves of the 2022 and 2023 seasons. 

Inflated spin rates stemming from the experimental, pre-tacked baseballs serve as the most likely explanation for the rise in strikeouts and decrease in batting average. Higher spin rates can be attributed to an increase in friction, according to Alan Nathan, professor emeritus at the University of Illinois, whose research focuses on the physics of baseball.

“The primary thing is the friction between the fingertips and the surface of the ball,” Nathan said. “And by increasing that by having a sticky substance on the ball, that friction increases and as a result, you get more spin.”

That means more movement on pitches. Putting a tacky substance on a baseball could add three pounds of friction, increasing the spin rate of an 85 mile per hour curveball by about 17 percent, according to John Eric Goff, professor of physics at the University of Lynchburg. 

That added spin causes the pitch to drop an additional two inches, which can make all the difference given the width of a bat barrel, Goff said. According to the MLB rulebook, a baseball bat can be no wider than 2.61 inches in diameter.

“If all the sudden everything looks the same, but the ball is dropping an extra couple of inches, what you might be able to time in the past into the sweet spot of the bat is going to be either missed or you're just going to be able to hit a very weak grounder or something like that,” Goff said.

For fastballs, thrown with backspin compared to the topspin of a curveball, more spin creates less drop. A fastball never truly travels upwards, but when it doesn’t drop as much as expected, it appears like the pitch is rising, Goff said. For hitters, it can be baffling.

“It's going to drop a little less, so you're going to have batters possibly swinging under pitches and missing them that way whenever they're swinging at fastballs,” Goff said.

More movement, less control

Based on what’s been previously observed when pitchers throw with sticky substances on their fingers, a tackier ball leading to higher spin rates and increased strikeouts makes sense, according to Andy Andres, senior lecturer at Boston University.

“Certainly the big thing is you should be able to get much higher spin on these balls, and that means more break,” Andres said. “So that should mean more strikeouts.”

But the Southern League also saw a jump in walks and wild pitches from 2022, a more surprising trend.

The rate of walks per nine innings in the first half of the 2023 season rose 15 percent compared to the first half of the 2022 season. Wild pitches saw an increase of more than 13 percent.

Andres said there could be a learning curve in pitching with a new, different ball. But an increase in walks and wild pitches is not normally what he would consider the outcome of a pitcher utilizing a sticky substance. 

“If you had said, ‘Hey what do you predict given all you know?’ I would not have predicted that,” Andres said.

More movement on pitches might partially explain the trend. Josh Herzenberg is the manager of player personnel at Driveline Baseball, a data-driven player development company. He said that commanding pitches would become more difficult for players not accustomed to the increased movement profile of their pitches.

Moreover, a pitcher who has reached the Double-A level likely already has a foundation for who they are in terms of “proprioception,” the ability to sense the movement and position of one’s own body. 

“And so, as a result it would probably be a little bit of an adjustment,” Herzenberg said.

The experimental ball simply being different from what Southern League pitchers were previously used to throwing can also explain the jump in walks and wild pitches. 

Tohoku University professor Takeshi Yamaguchi studied the effect of grip-enhancing agents on the friction between a fingertip and the surface of a baseball. 

He said it’s believed that “each individual may have a range of friction coefficients that are easy to control and maximize performance.” 

If the friction between the fingers and the experimental baseball falls outside that range, a pitcher would need to adjust their throwing motion. With this, some players may be able to adapt while others cannot.

“If you try to throw a high-friction ball and a low-friction ball at the same place, at the same speed, and with the same number of revolutions, the throwing motion will be different,” Yamaguchi wrote in an email. “The change in friction means that the throwing motion needs to be adjusted again.”

Herzenberg, who’s previously worked in player development and scouting for MLB and Korea Baseball Organization teams, said that while experimentation is good, he’d prefer a uniform baseball across all leagues.

“It’s probably not the best way to optimize development to have one league to use a different baseball,” Herzenberg said.

Mudding the baseball

Jim Bintliff was 9 years old the first time he shoveled the mud. He was with his grandfather then. In 1980, at age 23, he took over the business, namely harvesting and shipping, from his father, who himself had been shoveling the mud since 1965.

About twice a month unless the ground is frozen, Bintliff, 66, still treks through the woods in New Jersey to a secret spot along a Delaware River tributary. He goes down on foot to the riverbank and shovels the mud there into buckets, screening it to remove any foreign debris. He drains the river water off the mud and replaces it with fresh water. 

Eventually, the mud is sold and shipped to countless teams and leagues, who use it to break in and add grip to brand-new baseballs. 

“Superior grip means superior control,” reads the container label of Lena Blackburne Original Baseball Rubbing Mud. “The preferred de-glossing agent for professional baseball since 1939. Used in sandlots and ballparks around the world!”

Sitting in its plastic container, the rubbing mud is dark brown and just slightly moist. On the fingers, it feels like a rough, gritty clay. Then it quickly dries out, becoming a fine dirt dust. 

A jar of Lena Blackburne Original Baseball Rubbing Mud sits open before a game at Ozinga Field in Crestwood, Illinois. The substance is rubbed on “pearls,” brand-new white baseballs, to give the sleek and slippery balls more grip. Erez Ben-Akiva/Medill

From Jim Bintliff’s shovel, the material might end up in the fingertips of someone like Angel Rivera, clubhouse manager for the Kane County Cougars, a member of the American Association of Professional Baseball. 

Before a game, Rivera “rubs up” eight dozen Rawlings baseballs. During a game, he’ll rub up another five dozen. 

“What I do is I put just a line, like a small line on all four corners of the ball, and then I just rub it all together to mix it in and make the ball less slippery,” Rivera said. 

It’s far from a standardized process. Clark Morgan, the Frontier League umpire, said there are “different philosophies” for rubbing mud on a baseball.

“What seems to be what most guys do and what we do is you take a small bit of mud and apply it to each side of the baseball, and then you just rub the baseball down with each hand,” Morgan said. “There's no way to measure it, but a precise combination of mud and water, over time you just kind of get a feel for it.”

In June 2022, MLB issued a memo to all teams in an effort to make the pre-game rubbing more uniform. It outlined that club staff members should ensure each baseball received the same mud and water ratio rubbed on for at least 30 seconds, according to the Associated Press.

The memo also stated that balls should be mudded on the day of the game in which they are intended to be used. 

Dan Straily, who pitched in the MLB until 2019 before heading to the Korea Baseball Organization, said he would ask major league staff to rub the baseballs closer to when they would appear in a game, though he didn’t think it usually happened.

“A lot of times they rubbed the balls up like weeks in advance, and so everything is just super dry by the time they get to the games anyway,” Straily said. “Every ball was different. I mean, it was very inconsistent.”

Too little or too much mud can also lead to complaints from players. Both Rivera and Morgan said that rubbed up baseballs might remain slippery or become colored too dark for use. It’s largely for those reasons why a pitcher might discard a new baseball during a game.

As Washington Wild Things players streamed past him down the hallway after completing  batting practice, Morgan said that the primary goal is to avoid rubbing mud in the laces, so as not to affect the flight of the baseball, like a chunk of mud in the seams that might alter the movement of a breaking ball. 

“We just try to make sure that there's nothing on it that’s sticking up or staying out, as far as the baseball or what its path might be,” Morgan said. 

For Morgan, consistency from baseball to baseball is the desired result.

Bintliff though is not convinced that consistency should be the ultimate goal of the game. A level of human variability has always existed within the relationship between pitcher and batter.

“Analytics took over the game,” Bintliff said. “Their goal is to make everything identical, and they feel that different teams rub the balls differently. Use more or less mud. Make the balls darker or lighter. And they want to do away with that variable. Give it another 10 years they’ll be using pitcher machines. That'll be it.”

Pre-tacked baseballs overseas

While Major League Baseball experiments in the minor leagues with potential alternatives to Jim Bintliff’s rubbing mud, professional leagues in other countries have embraced pre-tacked balls.

The Korea Baseball Organization in 2016 adopted a pre-tacked ball produced by the baseball equipment company Skyline, according to Dan Kurtz, founder of KBO fan site mykbo.net. 

Japan’s Nippon Professional Baseball utilizes a pre-tacked ball manufactured by sporting goods company Mizuno. Indeed, upon its league-wide issuance in 2011, the Mizuno baseball resulted in an “abundance of curiosities,” like noticeably lower earned run and batting averages, as described by Brad Lefton in the New York Times.

The experimental Southern League ball, in comparison, is a Rawlings baseball tacked with a proprietary Dow chemical substance.

“I don’t recall ever speaking to a pitcher who prefers the current iteration of a major league baseball over a KBO or NPB ball,” Herzenberg said. “Those guys are pretty steadfast in their belief that those are the best.”

According to Herzenberg, KBO baseballs do not require any rubbing up. They come out of the box completely white and can be given directly to the pitcher. 

“Tackier, easier to grip and more consistent,” Herzenberg said as he demonstrated gripping a non-mudded MLB ball, an NPB ball and a KBO ball over Zoom.

Herzenberg rubbed his thumb across the MLB ball, showcasing the slippery, slick nature of the leather, then did the same to a KBO ball. 

“I can obviously still do it, but it’s just a little more difficult to rub my finger across it, so it’s just a little more grippier,” Herzenberg said. “It’s kind of like if you’re in the weight room and you’re lifting a heavy weight without chalk versus with chalk. It’s just a little bit more comfortable to grip with chalk because there’s a little bit more of a consistency in your hand.”

Tohoku University professor Takeshi Yamaguchi found that the leather of the NPB baseballs is thicker and softer than MLB baseballs. Moreover, NPB balls on their own showed “comparative friction” to MLB balls covered in a sticky substance.

“This means that the NPB ball is very, very high friction compared to the MLB ball,” Yamaguchi said.

Meanwhile, mudding MLB balls was found to not have a significant effect on the friction coefficient.

“By mudding, some mud particles on the surface, that will change the perception of the pitcher,” Yamaguchi said. “But in terms of just a physical friction coefficient, mudding doesn’t affect very much.”

While mud might not be found on the baseballs used in Japan and South Korea, Bintliff said he sells his product overseas. Former MLB manager Bobby Valentine, who in 1995 and from 2004 to 2009 managed NPB’s Chiba Lotte Marines, bought the mud and brought it with him to Japan, Bintliff said. 

Bintliff has heard from managers who coached in the Arizona Fall League, where enhanced grip baseball experiments have also run in recent years. 

“They say, ‘My pitchers don't like it. My pitchers want to put mud on it anyway. The feel is much better with the mud on it,’” Bintliff said. “But they’re not the ones that are going to decide.”

Nonetheless, pitchers who have played in both MLB and KBO seem to prefer the pre-tacked Skyline baseball. 

“It’s pretty unanimous across the board,” Herzenberg said.

Nick Kingham, for example, racked up more than 130 major league innings for the Pittsburgh Pirates and Toronto Blue Jays in 2018 and 2019. He went to South Korea in 2020 and has pitched with the SK Wyverns and Hanwha Eagles.

“The MLB ball is the most difficult ball I’ve ever thrown with,” Kingham wrote in a message. “It’s firm like a cue ball, and once it gets wet from sweat, it becomes slippery from the mud. Asia has the best balls. They’re slightly tacky but not sticky. Just enough to not let it slip out of your hand!”

Dan Straily agreed with the cue ball assessment. 

“That’s 100% accurate,” he said. 

Pitchers transitioning from MLB to KBO do often see a spin rate increase, according to Herzenberg. Straily also said he had a higher spin rate pitching in South Korea.

But the KBO hasn’t seen the same issues, like inflated strikeouts and walks, that emerged in the Southern League.

“It’s not an issue in the KBO largely because I think the guys are probably used to it,” Herzenberg said. 

Perhaps then it would simply be a matter of time until players in the minor leagues and MLB adjusted to the pre-tacked Dow baseball.

Kurtz similarly has not noticed any changes in play or statistics since the KBO first introduced the Skyline baseball in 2016. Any year to year differences probably cannot be attributed to the ball.

“It’s going to be playing level that would probably be the difference as to why there may be some increases or even decreases,” Kurtz said.

MLB owns Rawlings, the company that manufactures major league baseballs, which might explain why it turned to Dow to develop a substance for the balls rather than commissioning Skyline or Mizuno for their baseballs. 

“How hard is it for Rawlings to be like, ‘Hey guys, Skyline makes a pre-tacked baseball in South Korea. How do they do it? It’s not rocket science. We could do something similar,’” Kurtz said.

For his part, Bintliff doesn’t know how much he would miss the business from MLB, were the league to adopt a pre-tacked ball in the future. He sells “tankers full of mud” to football teams, giving him steady business year-round. 

So for now, rubbing mud remains integral to the preparation of MLB baseballs, not to mention the vast landscape of American baseball outside the majors. 

In between innings of the mid-summer Saturday evening game between the Washington Wild Things and Windy City Thunderbolts of the Frontier League, a young bat boy lugged the white plastic bucket filled with mudded baseballs towards home plate umpire Reid Hoover.

Standing a few feet in front of the first base dugout, Hoover looked down into the bucket momentarily, eyeing the pile of rubbed up baseballs. Having made his selection, he grabbed a couple of the balls, using the inside of his protective mask to hold them. Then he turned back to the baseball diamond, as Wild Things starting pitcher Justin Showalter fired a warm-up pitch towards home plate.