Only rosin is allowed to get on the baseball in MLB

Pitchers aren’t allowed to put any foreign substance directly on the baseball and rosin is the only substance they can put on their hand.

If baseball fans weren’t familiar with ‘sticky’ or ‘foreign’ substances before, they are now. Amid a season of historic pitching success powered by no-hitters and strikeouts, sticky pastes and powders, like one called Spider Tack, have recently been blamed by batters for increasing the spin and movement of pitches.

The back-and-forth about these substances can easily be confusing. Coverage of the debate says some substances are “long-accepted, if not technically legal” while also quoting players and managers who want Major League Baseball to crack down on illegal substances.


Does Major League Baseball forbid pitchers from applying foreign substances, like Spider Tack, to baseballs?



This is true.

MLB rules forbid pitchers from applying any foreign substance directly to baseballs. Pitchers are allowed to put rosin, a sticky powder made from pine tree sap, on their hands to better grip the baseball, but aren’t allowed to put anything else on their hands because it could get on the baseball. 

Pitchers have historically used such substances to control the ball better, but MLB says they’re now using it to get more speed and movement on their pitches.


The 2021 MLB rulebook specifically forbids the use of foreign substances on baseball in multiple sections.

Rule 3.01, on page five, says: “No player shall intentionally discolor or damage the ball by rubbing it with soil, rosin, paraffin, licorice, sand-paper, emery paper or other foreign substance.” 

Rule 6.02(c), on page 78, says the pitcher shall not “apply a foreign substance of any kind to the ball.”

A comment beneath Rule 6.02 makes an exception for rosin: “A pitcher may use the rosin bag for the purpose of applying rosin to his bare hand or hands. Neither the pitcher nor any other player shall dust the ball with the rosin bag.” 

Pitchers aren’t allowed to combine rosin with sunscreen, and the league recommends they don’t apply sunscreen after sunset in games.

So MLB makes it very clear that this stuff isn’t allowed. So what’s the controversy? Why is it still being used?

A June 15 press release from MLB, which stated umpires would enforce these rules more strictly with more frequent checks, acknowledged the history behind these substances. 

“I understand there’s a history of foreign substances being used on the ball, but what we are seeing today is objectively far different, with much tackier substances being used more frequently than ever before,” Commissioner Rob Manfred said in the press release. “It has become clear that the use of foreign substance[s] has generally morphed from trying to get a better grip on the ball into something else – an unfair competitive advantage that is creating a lack of action and an uneven playing field.”

A pitcher can grip a baseball covered in something sticky better than they can grip a baseball normally. According to Alan Nathan, a physics professor at the University of Illinois, that gives the pitcher two advantages: more spin and more control.

“Spin is created by the friction between the pitcher’s fingers and the surface of the baseball,” he explained. “When there’s friction, the fingers sort of stick to the ball.”

A downward motion on the ball creates backspin, which applies an upward force to the ball that fights the downward pull of gravity and reduces the drop on the ball. The opposite motion creates topspin, which makes the ball drop even more than it would if gravity was the lone force acting on the ball. So the pitcher controls the ball’s movement with spin, and more spin means more ball movement on a pitch.

“The total amount of movement, as well as the direction of the movement, are things completely under the control of the pitcher,” Nathan said. “He decides how he wants that ball to move, and [does so] in a way that keeps the batter guessing. So definitely, putting spin on the ball gives the pitcher a distinct advantage.”

But the other benefit of grip, control, is the reason that there wasn’t any controversy around the use of these banned substances until recently.

“If the ball is slipping as [the pitcher] releases it, it could go off in some crazy direction and it could be a danger to living people,” Nathan said. “So, up until recently, everyone knows everyone’s [using foreign substances on the ball], but nobody’s really complaining about it. And as a matter of fact, batters would prefer that pitchers have better control, so that they’re not going to get hit in the head.”

That was the main concern of Yankees pitcher Gerrit Cole, one of the players accused of increasing his spin rate with substances like Spider Tack, when he spoke in a press conference following a game he pitched on June 16.

“It’s so hard to grip the ball,” Cole said. “For Pete’s sake, it’s part of the reason why almost every player on the field has had something, regardless if they’re a pitcher or not, to help them control the ball.”

Major League Baseball said in its press release it was amping up enforcement of this rule because data suggested because the substances were contributing “to a style of pitching in which pitchers sacrifice location in favor of spin and velocity, particularly with respect to elevated fastballs.” It said 2021 has had the “highest rate of hit-by-pitches of any season in the past 100 years.”

Instead, MLB claimed its research concluded “foreign substances significantly increase the spin rate and movement of the baseball.”

Nathan warned that he would be “cautious about drawing strong conclusions about why the strikeout rate has increased.” He said in his own study looking at “basically every pitch thrown in Major League Baseball over the last few years,” he’s found that the spin rate has increased by 1-1.5% between 2019 and 2021. Over the same period of time, the movement on a four-seam fastball has increased between 4-4.5%.

That’s a sentiment Cole, who wants the league to choose a legal ‘universal substance’ besides rosin all pitchers can use, tried to argue in his press conference, too. 

“Spin rate is not everything,” he said after he earned a win. “You can still pitch well if you don’t have a high spin rate.”

The remainder of the 2021 season will serve as an informal test of Cole’s claim. Foreign substances were already banned at the start of the season, but now the league’s new enforcement policy will make sure no one uses the substances anyway.

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