A Whole New Ballgame?

Without a doubt, the most thrilling part of a baseball game is watching a player bash a ball out of the park. And if you caught a game last year, there’s a good chance you saw at least one home run. That’s because in 2019, Major League Baseball (MLB) players hit a total of 6,776 homers—nearly 700 more than the previous record, which was set in 2017.

A staggering 14 out of 30 teams set franchise records for home runs last year, with four teams setting records for the most home runs ever hit in a single season. Since 2014, the MLB home run rate has increased by more than 62 percent. Some players, coaches, and scientists believe the uptick in homers has to do with changes to the materials used to make baseballs, which could affect how far they fly.

What’s the most exciting part of a baseball game? No doubt, it’s watching a player hit a ball out of the park. And if you watched a game last year, you probably saw at least one home run. That’s because Major League Baseball (MLB) players hit a total of 6,776 homers in 2019. That number is nearly 700 more than the old record, which was set in 2017.

It seems amazing, but 14 out of 30 teams set franchise home run records last year. Four teams had the highest single-season home run season in history. Since 2014, the MLB home run rate has grown more than 62 percent. Why the increase in homers? Some players, coaches, and scientists believe it’s connected with changes to the materials used in baseballs. Those changes could affect how far they fly.

However, after looking into the issue, MLB released a report in 2018 that stated the contrary. It concluded that balls were indeed sailing farther than in the past, but that no changes to the balls’ manufacturing could account for increased home run rates. MLB theorized that players’ shift to hit more fly balls than grounders had led to the rise in home runs.

Still, baseball experts had their doubts. Many wondered: Had baseballs been secretly altered to increase the number of home runs? That, people speculated, would make games more exciting, which in turn could boost ticket sales and TV viewership. “Few things in baseball are as dramatic as a home run,” says Meredith Wills, a sports data scientist at SportsMEDIA Technology in California. “With one swing of the bat, the entire game can change.” So Wills and other researchers began to dig deeper to uncover whether something more was at play.

But MLB looked into the question. In 2018, it released a report that said the opposite. Balls were flying farther than before, and home run rates had increased. But MLB said that no changes to the balls’ manufacturing could explain this. Players had started hitting more fly balls than grounders. MLB thought this had caused the rise in home runs.

But baseball experts still wondered. Had baseballs been secretly changed to increase the number of home runs? People thought this would make games more exciting. Then ticket sales and the number of TV viewers would rise. Meredith Wills is a sports data scientist at SportsMEDIA Technology in California. “Few things in baseball are as dramatic as a home run,” she says. “With one swing of the bat, the entire game can change.” So Wills and other researchers began to dig deeper. They wanted to find if something more was involved.

Scientists like Wills first began noticing the number of home runs increasing in the middle of the 2015 season (see Going Up). After the 2015 All-Star Game—the halfway point of MLB’s calendar—a new batch of balls had been delivered to teams. Suddenly, home runs skyrocketed.

Pitchers also began reporting that balls felt different. They said the seam, where the two pieces of leather that cover the ball are stitched together, felt more pronounced. Pitchers also began experiencing more blisters on their fingers where they grip the ball at the seam. This injury can derail an athlete’s entire season, or worse. “It’s quite likely the pitching blisters he got during this time ended Aaron Sanchez’s career,” says Wills. Sanchez was a pitcher for the Toronto Blue Jays and Houston Astros.

Scientists like Wills first noticed a difference in the middle of the 2015 season. That’s when the number of home runs started growing (see Going Up). The 2015 All-Star Game was the halfway point of the MLB season. After that, new balls were delivered to teams. Suddenly, home runs shot up.

Pitchers also began reporting that balls felt different. Two pieces of leather cover the ball. They’re stitched together at the seam. Pitchers said the seam felt more pronounced. They also started getting more blisters on their fingers where they grip the ball at the seam. This injury can end an athlete’s entire season, or worse. “It’s quite likely the pitching blisters he got during this time ended Aaron Sanchez’s career,” says Wills. Sanchez was a pitcher for the Toronto Blue Jays and Houston Astros.

To see if the baseball’s design had been altered, Wills took apart balls from before and after the home run surge—something MLB neglected to do for its 2018 report. She measured and compared 16 different variables between the two. Only one factor stood out from the rest: The iconic red laces used to stitch together the newer balls’ leather covers were about 10 percent thicker than those of older balls.

A thicker string has a higher tensile strength. That’s the amount of force a material can withstand while being stretched without breaking. The thicker laces caused the balls’ leather covers to be sewn tighter, which made their shapes more spherical. A rounder ball experiences less drag, which is the slowing force of air pushing against an object as it moves. This makes the ball more aerodynamic, so it can fly farther when hit.

No one is sure why the baseball manufacturer started using the thicker laces. Wills believes Rawlings, the company that manufactures the ball at a facility in Costa Rica, simply found a vendor that sold these laces for less. The company likely didn’t think such a small change would affect the overall design and performance of the ball. Wills thought she’d solved the home run mystery. Then in 2019, home run numbers spiked for a second time.

Wills wanted to see if the baseball’s design had been changed. So she took apart balls from before and after the home run rise. MLB hadn’t done that for its 2018 report. She measured and compared 16 different variables between the two. Only one factor stood out. It was the famous red laces used to stitch balls’ leather covers. The laces of the newer balls were about 10 percent thicker than those of older balls.

A thicker string has a higher tensile strength. That’s the amount of force it can withstand while being stretched without breaking. The thicker laces caused the balls’ leather covers to be sewn tighter. That made their shapes rounder. Drag is the slowing force of air pushing against a moving object. A rounder ball experiences less drag. This makes the ball more aerodynamic, so it can fly farther when hit.

Why did the baseball manufacturer start using the thicker laces? No one is sure. Rawlings is the company that makes the ball at a factory in Costa Rica. Wills believes Rawlings simply found a vendor that sold these laces for less. It was such a small change. The company probably didn’t think it would affect the ball’s overall design and performance. Wills thought she’d solved the home run mystery. Then in 2019, home run numbers rose again.

In 2018, MLB bought the Rawlings company. League officials said that gave MLB “even more input and direction on the production” of the ball. Around the same time, Triple-A minor league teams started using the same balls as big-league clubs. So MLB “needed to make a lot more balls in the same amount of time,” says Wills.

By the end of 2019, minor leaguers had hit nearly 60 percent more home runs than in 2018. And MLB players reported again that the ball felt different. Many pitchers, such as Sean Doolittle of the Washington Nationals, said the ball felt slicker and harder to grip.

MLB bought the Rawlings company in 2018. That gave MLB “even more input and direction on the production” of the ball, said league officials. Around the same time, Triple-A minor league teams started using the same balls as big-league clubs. So MLB “needed to make a lot more balls in the same amount of time,” says Wills.

By the end of 2019, minor leaguers had hit nearly 60 percent more home runs than in 2018. And MLB players reported that the ball felt different again. Washington Nationals pitcher Sean Doolittle said the ball felt slicker and harder to grip. Many pitchers said the same thing.

Wills studied the balls and made a surprising find: The red laces were back to their original thickness. Unlike in 2015, this variable couldn’t explain why there were more home runs in 2019. However, the seams on the 2019 ball were significantly flatter than balls used before 2019.

Next, Wills examined the ball’s leather cover. It was the exact same material always used in the modern baseball era. But since pitchers complained about the ball’s slipperiness, Wills decided to test the leather’s smoothness. Wills removed a ball’s cover and placed the material on a smooth wooden plank. She then gradually tilted the board. Once the leather cover began to slide down the plank, Wills measured the board’s angle. A smaller angle corresponds to a lower amount of static friction— measurement of how much resistance a surface exerts on another surface sliding against it—meaning that object has a smoother surface. Wills found that the static friction of the 2019 ball was about 28 percent less than that of the older balls, though it’s not clear what caused this.

Wills studied the balls and found something surprising. The red laces were back to their original thickness. This variable couldn’t explain the rise in home runs in 2019, like it could in 2015. But the seams on the 2019 ball were much flatter than on older balls.

Next, Wills studied the ball’s leather cover. It was the exact same material always used for modern baseball. But pitchers complained about the ball’s slickness. So Wills decided to test the leather’s smoothness. Wills removed a ball’s cover and placed the material on a smooth wooden plank. Slowly, she tilted the board. When the leather cover began to slide down the plank, Wills measured the board’s angle. A smaller angle shows a lower amount of static friction. That’s a measure of how much one surface resists another surface sliding against it. And less static friction means that object has a smoother surface. Wills found that the static friction of the 2019 ball was about 28 percent less than that of the older balls. But it’s not clear what caused this.

Normally, to get the leather cover to stretch tightly around the outside of the ball, workers first soak the material in water and then leave it to air-dry for about two days. “It looks like MLB decided to speed up drying by using some sort of heating process,” theorizes Wills. Cutting down the manufacturing time would allow MLB to produce more balls. Previously, Rawlings produced about 1.2 million balls each season. But with the additional demand from the minor league, Wills says, production was increased to at least 1.5 million balls for both leagues.

If Wills is right, it would explain why the balls’ seams were flatter than usual. During the heating process, the red cotton laces would shrink, pushing down on the seams to flatten them. That, in turn, pulled the ball into a rounder shape, making it more aerodynamic. “It’s like if you hung a T-shirt out on a line to dry and it got a little stretched out, compared with drying it in a drying machine and the material shrinks,” says Wills.

Rawlings’s goal, says Wills, is to “make a ‘good baseball’ with smooth leather, that’s round, and has low seams. It turns out they made a perfect baseball, which is bad for MLB–especially for pitchers.” Wills’s discovery, though, is only part of the story.

Workers must get the leather cover to stretch tightly around the outside of the ball. Normally, they soak the material in water first. Then they leave it to air-dry for about two days. “It looks like MLB decided to speed up drying by using some sort of heating process,” guesses Wills. If they cut down the manufacturing time, MLB could produce more balls. Rawlings used to produce about 1.2 million balls each season. But now more balls are needed for the minor league. Wills says production was increased to at least 1.5 million balls for both leagues.

Wills’s idea would explain why the balls’ seams were flatter than usual. During the heating process, the red cotton laces would shrink. They would push down on the seams to flatten them. And that would pull the ball into a rounder shape, making it more aerodynamic. “It’s like if you hung a T-shirt out on a line to dry and it got a little stretched out, compared with drying it in a drying machine and the material shrinks,” says Wills.

Wills says Rawlings’s goal is to “make a ‘good baseball’ with smooth leather, that’s round, and has low seams. It turns out they made a perfect baseball, which is bad for MLB–especially for pitchers.” But Wills’s discovery is only part of the story.

In 2018, a friend and sports science researcher asked Nathan Beals if he could help look into the chemical makeup of MLB’s baseball. At the time, Beals was a biomedical researcher at Kent State University in Ohio. While scientists like Wills had researched physical differences between old and newer balls, no one had studied changes to the chemistry of the materials.

Beals examined the balls used before the 2015 All-Star Game and in 2017 using a CT scanner. This medical-imaging technology uses high-energy X-rays to take pictures of structures inside an object. Like Wills, Beals discovered obvious differences between the balls. The dimensions of the balls’ center, called the pill, were the same (see Baseball: Inside & Out). But he found a greater number of air bubbles within the rubber of the newer ball. That made the newer ball’s pill about 57 percent less dense than that of the older ball.

In 2018, Nathan Beals got a request. A friend and sports science researcher asked him to help study the chemical makeup of MLB’s baseball. At the time, Beals was a biomedical researcher at Kent State University in Ohio. Scientists like Wills had looked into physical differences between old and newer balls. But no one had studied changes to the chemistry of the materials. 

Beals looked at the balls from before the 2015 All-Star Game and from 2017. He used a medical-imaging technology called a CT scanner. It uses high-energy X-rays to take pictures of structures inside an object. Like Wills, Beals found clear differences between the balls. The balls’ center is called the pill. Its measurements were the same (see Baseball: Inside & Out). But he found more air bubbles in the rubber of the newer ball. That made the newer ball’s pill about 57 percent less dense than the older ball’s.

“The density of the ball can potentially correlate with how bouncy it is,” says Beals. And that could also help explain why newer balls could rebound off the bat faster when hit. Like Wills, Beals believes manufacturing changes might explain why the pills differ. In 2015, when the home run surge was first seen, Rawlings replaced old molds used to make pills with newer ones, which could have affected their composition.

Even though the mystery behind MLB’s spike in home runs may have been solved, the changes to MLB balls have left many feeling uneasy going into the 2020 season. (As of press time, the start of the 2020 season has been suspended for at least two weeks due to the spread of the novel coronavirus.) “Teams and players are unhappy because they don’t know what ball to plan for,” says Wills. Baseball fans, too, are unsure what to expect: Will home runs dip this season or will balls continue to sail out of the park at the same rate?

“The density of the ball can potentially correlate with how bouncy it is,” says Beals. And that could help explain the increase in home runs. The newer balls could bounce off the bat faster when hit. Like Wills, Beals believes manufacturing changes might explain the difference in the pills. Molds are used to make pills. In 2015, Rawlings replaced the old molds with newer ones. That could have affected the pills’ makeup. And that year is when the home run rise first happened.

The mystery behind MLB’s spike in home runs may have been solved. But many feel uneasy about all the changes to MLB balls going into the 2020 season. (As of press time, the start of the 2020 season has been put off for at least two weeks. That’s because of the spread of COVID-19.) “Teams and players are unhappy because they don’t know what ball to plan for,” says Wills. Baseball fans also don’t know what to expect. Will home runs dip this season? Or will balls continue to sail out of the park at the same rate?