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Mark Hembree


Home Runs Were Up—Now They’re Down. Why?

Rumors about ball performance meet quality assurance

Published: Monday, August 29, 2022 - 11:03

‘Anyone can hit a home run if they try,” said the great Ty Cobb at the end of the deadball era as Babe Ruth rose to fame in the 1920s. Cobb was unimpressed by Ruth, the Sultan of Swat. “It’s a brute way to approach the game.”

In 2019, Major League Baseball (MLB) seemed to prove Cobb’s point as big leaguers whacked a record 6,776 home runs—671 more than any year in major-league history.

In previous years, there had been much scuttlebutt about the ball seeming livelier. But 2019 took the cake. That year, the MLB-standard ball was introduced in AAA baseball—and at the minor-league level, home runs soared at a major rate. Not since 2011 had there been more than 4,000 home runs in AAA. But in 2019 there were 5,749, up from 3,652 in 2018.

Consequently, minor changes were made in the manufacturing of the ball—giving rise to a new set of suspicions and theories.

Something must be done

Astute students of the game notwithstanding, everyone loves a home run. But MLB decided this was too much of a good thing, and Rawlings, MLB’s ball manufacturer, made changes to bring the ball more tightly within spec and the home-run count closer to the mean.

The pandemic made 2020 a throwaway year for stats, but 2021 saw a more-moderate 5,944 homers. That might have slowed the rumor mill—except that in February 2021, The Athletic’s Ken Rosenthal and Eno Sarris reported a memo from MLB commissioner Rob Manfred’s office stating, “In an effort to center the ball with the specification range for COR and CCOR, Rawlings produced a number of baseballs from late 2019 through early 2020 that loosened the tension of the first wool winding.”

COR is the “coefficient of restitution,” a measure of incoming speed (the pitch) to the outgoing speed (the hit) as the ball is pitched at 60 mph against a flat surface made of wood or metal. CCOR is the “cylindrical coefficient of restitution,” another measure of a ball’s resilience as it strikes a cylindrical surface (not a bat in the lab, but you get the idea).

Then, in November 2021, Business Insider and others reported that MLB had used two different types of balls that year—one allegedly bouncier than the other. The following spring, Rosenthal and Sarris were at it again, noting that home-run rates were down in April of the 2022 season.

Furthermore, humidors, which had been used in arid places such as Denver and Phoenix to help keep fly balls from flying out of the park, were standardized for all MLB venues.

So, what’s with the ball?

ASTM International’s ASTM F1887-14(2019)e1 is the “Standard Test Method for Measuring the Coefficient of Restitution (COR) of Baseballs and Softballs.” ASTM F2845-22 is the “Standard Test Method for Measuring Dynamic Stiffness (DS) and Cylindrical Coefficient (CCOR) of Baseballs and Softballs.” Other ASTM measures include tests for bat performance, different types of bats, moment of inertia, and center of percussion.

Is there a quality control problem causing the ball to fly farther or not? Could it be the ball’s core? The core winding? The height of the seams? What about the humidors? Aside from pitchers and batters, variances in ball performance might indicate a quality control issue. Quality Digest (we never sleep!) decided to investigate.

Washington State is at bat and on the ball

I spoke to Lloyd Smith, director of Washington State University Sports Science Laboratory. Smith and his team actually test bats—not balls—and of the 11 major federations that regulate amateur softball and baseball, 10 of those use WSU’s lab as their exclusive certification center.

Of course, you can’t do that without the ball. “If you don’t understand the ball well, then it’s hard to measure bat performance accurately,” Smith says.

He brushed past the recent speculation to explain how his lab measures ball performance. It’s less about the ball’s composition and more about aerodynamics: lift and drag.

“If you go back just a few years, the only way anyone ever got the lift or drag of a ball was in a wind tunnel,” he says. “And that’s a very logical thing to do. Lift and drag are routinely measured in wind tunnels for all sorts of things, for aircraft or things that fly. So people then used those same devices for the ball.

“The problem is if you put something in a wind tunnel, then you have to hold onto it, and if you want to measure the lift of a ball, the ball’s got to be spinning. So it turns out it’s difficult, if you’re trying to get really accurate measurements of lift and drag, to do that in a wind tunnel with a baseball.”

The technique WSU developed is similar to how the U.S. Golf Association tests balls. “We’re firing the ball with spin, and then we’re making very accurate speed and location measurements of the ball,” Smith says. “Changes in the ball’s speed can be used to get its drag, and then with changes in the ball’s location, vertically, you can get its lift.”

Flow measurement system at Delft University of Technology measures airflow of balls in free flight. Credit: WSU Insider.

With MLB very much interested in those calculations of lift and drag, Smith’s lab has refined the testing. “I guess you could say that we have the most accurate measurements of baseball lift and drag,” he says. “It’s now a standardized test that we do for ASTM.”

Speed measurement system at WSU that measures drag. 

Going, going, not gone...

What does Smith think of current hitting trends? And how would he explain fly balls being caught by outfielders instead of happy fans in the stands?

“It’s a really interesting perspective,” Smith says. “If you talk about changing the ball core, if that did change, it would explain the discrepancies in calling home runs, right? I’ll mention the speed that the ball comes off the bat, so we would have to worry about that.

“And the same thing with changing the ball weight, right? That’s going to change its launch condition. It could change its flight a little bit, but the weight changes to the ball have been very small, so that couldn’t be it.

“It almost has to be in the flight of the ball. It’s aerodynamic. I can’t think of anything else. If the weight of the ball changed significantly, that could be it. But that’s not changed. It’s got to be aerodynamic.”

Juice or no juice?

Nevertheless, the home run numbers in 2019 led to some “adjustments” to the MLB ball. When MLB authorized two different balls in the same season, how much variety did that introduce?

Not much, Smith says. While fans and pundits ponder the ball’s makeup, he thinks the issue of putting two different balls in play in 2021 is overrated.

“Rawlings made a conscious effort to make a slight change in the weight of the ball to get it closer to the nominal over the MLB spec,” he says. “But I wouldn’t call that two separate balls. And the amount of weight change was nothing, a very small change. Due to the large sample of balls, absolutely you would find balls of the same weight from before the weight change and after the weight change.

“Rawlings works very hard to keep the ball consistent. Things may change, but these are not conscious or intentional changes. We haven’t looked in great detail, but we have considered to some degree the effect of the surface of the ball on how it flies. The findings we have would suggest that the seams are important, and the panels of the ball, the leather, much less important. The ball may be slicker. Is that due to the way the leather was tanned? Is it due to the type of mud or the amount of mud, or the time between the ball mudding and the ball being put in play? All of those factors are in play there, and will likely affect the way the ball is thrown and how much spin it has in the throw. But it’s really going to have a negligible effect on how the ball can carry.”

But yeah, 2019

Nevertheless, the numbers did not lie in 2019: That year, the ball was soaring out of the park.

“I don’t think I can get into specifics with the ball aerodynamics,” Smith said. “I mean, I know the answer, right, because I do the testing, but I do that on behalf of Major League Baseball. I can say, historically, the drag of the ball has changed. And we’re interested in two properties, lift and drag.

“What we find, when you’re talking about a home run, is you’ve got to have a really large change in lift to make a difference. For drag, small changes in drag make a big difference. So, generally, when we’re worried about ball carry, we’re worried about changes in the ball’s drag.”

Smith nodded to the lead-up to 2019, MLB’s Year of the Dinger. “We started doing this seriously about five years ago, that’s about 2017. We might have reached back a little further, but that’s when we really started talking about this seriously. At that time, there were small changes in drag, but the changes were enough that it was affecting the offense of the game. And that was definitely happening.”

Smith says they never found the cause. “Rawlings was never able to identify any change in its process that caused the ball to change. But we measured differences in seam height, and that led to differences in drag. And that’s been documented. We wrote two reports that MLB has published with our findings there. So that’s all out there in the public domain. But in the last couple of years, we’ve not seen changes in the ball’s drag or in the seam height. They’ve been very consistent.”

While acknowledging the importance of seam height, Smith says there is virtually no variance now—and he’s confident in that observation.

“Here’s an example,” he says. “The seam is 0.035 in. high. That’s a small number. As engineers, we make stuff in the machine shop all the time. And when you’re trying to machine a part and have it be within .001 of an inch, that’s really hard to do. We don’t measure to an accuracy of less than 0.001 in. very often. So, to give you an idea of what one thousandth of an inch is, 0.001 difference in seam height is a measurable difference in how far that ball wants to travel.

“One thing that’s kind of amazing to me is that we can actually measure that. The baseball is soft, the seam is soft, you can disform it with your hand, yet we can measure that. And we do that in a noncontact method. We have a laser scanner that scans the entire surface of the ball, and we’re able to look at the entire seam. If you do that for enough balls and average it out, you actually get an accuracy that’s on the order of 0.001 in.

"We pay close attention to it. If seam height was changing significantly, we would see that in the drag of the ball. And right now, the last couple of years, we have not seen that. The ball has been amazingly consistent.”

Humidors for all

In 2022, all MLB parks must store game balls in humidors before play. Is it fair that the ball should behave the same in Atlanta as it would in Denver? Has MLB taken standardization too far?

“Whether it’s a good idea or a bad idea to use humidors, I won’t speak to that,” Smith says. “One can make an argument either way. I can see your argument, and I can see MLB’s argument to make it more consistent.

“But if you ask me what the humidor does to a ball in flight, you’ve got two things there. What is it doing to the launch of the ball coming off the bat, and then what is it doing to the flight of the ball. We know absolutely that the ball is sensitive to humidity in the way that it leaves the bat, and that affects the coefficient of restitution [COR] of the ball. So, if you’re in Arizona, and you are putting a ball in a humidor, that’s going to bring the coefficient of restitution down, and that ball isn’t going to come off the bat as fast. Alternatively, if you’re in Florida where it’s really humid, you’re going to be hitting a ball that’s drier, and those balls are going to be coming off the bat faster. We know that, MLB knows that.”

That point, however, is not necessarily a game changer, he explains. 

“But to your point, about being able to call the home run, we’re really worried about what humidity does to how a ball flies. I guess my first response is nothing—it does absolutely nothing. You could argue that it might do something to a ball flight, but I can’t believe that it would significantly degrade the ability to predict whether it’s a home run or not. If you live in a dry climate, and you now have a humidor, your ball is going to be a little heavier, which might cause it to fly a little farther at the same speed, and it’s slightly larger, but that change in diameter is so small I can’t believe that that would affect how far it flies.

“The primary effect of humidity is the speed coming off the bat. It’s really not going to do anything significant that would significantly affect its distance in flight.”

So there’s no smoking gun in the humidor.

How else to explain recent numbers

Still, the number of home runs was down in 2021, and way down in the first half of the 2022 season. Could there be other characteristics of the ball that would explain that?

“You might talk to a meteorologist,” Smith says. “I wonder if there’s something about climate change where the prevailing winds are changing directions. You know that could actually explain what you’re talking about. If there’s some wind direction that’s changing, that could be affecting the way the ball’s carrying.”

A notable trend is that, while home runs are fewer, the number of doubles has soared. Is it because balls that would carry over the fence are instead hitting the wall and staying in play? If they do, it’s usually a double.

Turns out that can be measured, too. Smith said, “[Physicist] Al Nathan and others will use the hit data and actually calculate drag information from the ball’s flight path. And if something has changed globally, that can be found. If something has changed in your own park, that can be measured, too. The way to answer your question would be to take the hit data and calculate drag coefficient out of it and see if there’s an anomaly there.

“They actually track the ball path as it comes off the bat. And by that ball path, that measures how much the ball slows down, and from that they get the drag. That’s done fairly routinely, and in fact that’s one of the things they compare. They compare the drag measurements in the laboratory to the drag measurements they get in play and see if there’s a correlation.”

Still, Smith sees no measurable difference. “I do not believe the discrepancies can be explained by changes in the ball drag. This seems to be a very boring year in terms of what’s going on with the drag of the ball.”

The future is ahead of us

As Yogi Berra (or, some say, Niels Bohr) said, “It’s tough to make predictions, especially about the future.” But at the 2022 All-Star break, the season’s halfway point, 2,978 homers had been hit. At that rate, the season total would be 5,956, which is well short of 2019’s record 6,776. At the same rate, there would be 9,092 doubles hit in 2022—the most since 2007 (9,197) and the third-most in MLB history.

But Smith and the data tell us it’s not the ball, and it’s not the bat. That leaves player performance as the most important set of variables remaining.

Berra had an expert opinion on this, too: “Pitching always beats batting,” he said, “and vice versa.”


About The Author

Mark Hembree’s picture

Mark Hembree

As an associate editor with Quality Digest, Mark Hembree brings a technical writing/editing background to covering the quality control/quality assurance industry. A former professional musician and longtime journalist, he has been a staff writer for marketing companies and an editor for sports and hobby magazines. He’s also written a book about his music days, On the Bus With Bill Monroe: My Five-Year Ride With the Father of Blue Grass (University of Illinois Press, 2022).