The average home-run count in Major League Baseball (MLB) saw a 17 percent uptick in 2015. MLB figured it was a blip in the data, but when baseballs kept flying out of its 30 parks at record rates, the league wanted to know why, eventually creating a panel in 2017 to investigate the phenomenon.
Lloyd Smith found the culprit: red cotton seams on a baseball. And it took some ingenious lab tools to determine that flattened seams made a difference in a baseball’s drag.
A professor at Washington State University’s (WSU) School of Mechanical and Materials Engineering, Smith had been working on a new concept for about a decade to track a ball’s lift or drag more accurately than with traditional wind-tunnel practices. His method yielded a fresh approach to propelling a ball forward, using light-gate technology to measure speed. Light-gate tech uses a curtain of light and sensors to track when an object passes specific points, allowing the device to track the speed of the object (or baseball in this case).
Coupling those tools with laser-mapping of a baseball, the WSU team came to a staggering conclusion: a .013-inch flattening of the red cotton seams on a Rawlings baseball reduced the ball’s drag, making a home run a higher probability. Smith and his team published their results earlier this year in the peer-reviewed journal Applied Sciences.
MLB has used the same ball manufacturer, Rawlings, for over 65 years. Even though the ball’s specifications haven’t changed in decades—featuring a carefully measured-out cork rubber pill, wrapped in layers of wool and covered with cowhide—the handmade properties leave it susceptible to minor differences. In other words, minor seam differences between baseballs could explain the major boost in home-run counts.
Traditionally, to track drag and lift data, researchers need to place a ball in a wind tunnel, but this requires attaching something to the ball—dubbed the stinger—to hold it in place. Smith says the wind-tunnel strategy has worked well for decades, but “if you’re really trying to capture drag accurately,” he tells Popular Mechanics, “the way you grab onto the ball can be a problem. It is hard to remove the effects of the stinger with a ball moving in the wind tunnel.”
WSU uses a high-end light-gate system to create a curtain of light on one side of the corridor the ball passes through, and a series of high-speed light-detector sensors on the other side to identify when an object passes by. With multiple signal points, a light gate determines the speed of the ball. “The speed measurement is not that hard, it is fairly straightforward,” Smith says, “it just has to be aligned carefully.”
With the light gate aligned, Smith and his team knew they needed something better than a traditional pitching machine to get the ball moving. While effective in batting practice, the wheels on the machine scuff the surface of the ball from the very first pitch. “The aerodynamics of the ball are very sensitive to the surface,” Smith says. “If you have a roughened ball, you’re worse off than [if] you were in the wind tunnel.”
Smith says the combination of the purpose-built cannon and high-caliber light gate allows the team to accelerate the ball to the desired speed, control the spin, and accurately measure lift and drag.
Smith started developing this method about a decade ago, and then worked with the National Collegiate Athletic Association (NCAA) on baseball specifications. When MLB created a panel, the league came calling. Smith says his team soon found that using a hand caliper to measure the seam height of soft cotton wasn’t precise enough. They configured a laser to take 10,000 data points of the ball to measure any differences between balls, including the ability to get an average height of the hand-sewn red cotton seam. Smith’s team then upgraded its laser readings to take over one million data points on every ball.
Now working with MLB on an ongoing basis, the new lab measurements of a baseball’s drag can work with basically any ball. The lab has researched multiple types of baseballs, softballs, golf balls, and even most recently a study looking at pickle-balls.
When it comes to baseball, Smith will be the first to know if those seam heights—or anything else—changes on a MLB ball. “There is a lot of fun, interesting aerodynamics you can do when you get this really precise measurement,” he says.