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Brandon Shulista isn’t sure how a breaking pitch works. He just knows that when he holds his fingers along the seams in a certain way and flicks his wrist when he throws, the ball travels in a way that he has an idea where it’s going, but the batter doesn’t.
And that gives him a decided advantage.
“It’s tough for the batter because they want to back out when they see a curveball, and then it drops back in over the plate for a strike,” says Shulista, a junior pitcher on the Hawkeye baseball team who’s been throwing breaking pitches since he played for Solon High School.
Pitchers have an array of breaking pitchers at their disposal—curveball, slider, cut fastball, sinker—all designed to confuse the batter into thinking the ball is going one place, when in fact it’s going to another.
Some of them—like the curveball or the sinker—are slow pitches with big, dramatic breaks that the batter can see, but can only guess as to where the ball will be when it reaches his bat. The slider and the cutter are thrown with the same speed as a fastball and have much less dramatic breaks, but the ball is moving so fast that even as it moves only an inch or two, the batter has already committed to swinging at Point A as the ball crosses the plate at Point B.
Shulista uses both pitches regularly, but favors the slider.
“It looks like a fastball and the late movement confuses the batter,” he says.
But what’s the science that makes a slider slide and a curveball curve? Ken Gayley, associate professor of physics and ardent Dodgers fan, says it’s a basic fluid dynamics question, just like what makes a plane fly or a sailboat slip through the waves or an empty plastic bag on the side of the road fly up in the air when a car drives by. But explaining that is not always so simple. If you’re talking math, a scientist can do it easily enough. Gayley says most physicists agree the Navier-Stokes Equations do a nice job of explaining the breaking pitch. But using words, it’s not so easy.
“There’s the ‘shut up and calculate’ approach to physics, where I run the numbers and I have a curveball,” he says. “But sometimes, the problem is that numbers and the English language don’t talk to each other too well, then sometimes you have an issue.”
So physicists don’t have a universally accepted textual explanation for what makes breaking pitches break. But there is general agreement on certain factors: the speed the ball is thrown; the tightness of the curve; and stitches. The curveball is thrown with a tight curve, but at a slower speed than a fastball so the ball has enough time to actually curve before it reaches the plate. Sliders and cutters are thrown with a tight spin but with the same velocity as a fastball, which means the ball has less break, but it happens so late it fools the batter.
But the most important factor in throwing a breaking pitch is the stitches. When New York City’s social elite were developing the game in the mid-19th century, they sewed the ball closed with stitches because it was the easiest way to hold the cover around the core. It was a pragmatic decision because that was about the only way they had to close a ball at the time, but it would change the way the game was played decades later.
Gayley says the stitches increase the size of the Boundary Layer around the ball as it moves through the air. The Boundary Layer is a micro-thin layer of air that surrounds an object in motion, the size of which depends on the speed of the object and its width. A wider Boundary Layer means a larger cushion of air so the surface of the ball makes less direct contact with the air it’s passing through. This creates less friction to slow the object, allowing it to travel further, and making it easier to control once it’s been sent forward.
On a baseball, the stitches poke out from the ball just far enough to create a sizeable air pocket that reduces friction between the surface of the ball and the air it passes through.
Without stitches—if the ball had a smooth surface, like a croquet ball—the ball would encounter so much friction it would not travel as far when hit, or be as easy for a pitcher to control when thrown. But because of the stitches, pitchers can throw breaking pitches and batters can hit home runs, a serendipitous effect of those 19th century New Yorkers sewing their first baseballs.
Once the stitching has been accounted for, Gayley says the baseball moves in all likelihood because of the Magnus Effect, the principle of physics that explains how spin affects the direction of an object in motion. Gayley says spin is important because, when a ball spins, the speed is higher on one side than the other, relative to the air around it. The air on the faster side of the ball makes less contact with the surface and it becomes more turbulent. Meanwhile, on the other side of the ball, the relative speed is lower, the air makes better contact and tends to “stick” to the ball as it follows the curvature of the surface. The air is then deflected either upward or downward, depending on which way the ball is spinning.
On a fastball, which is thrown with backspin, the bottom of the ball has a higher relative speed than the top, so the slower air passing over the top of the ball makes better contact. That air follows the curvature of the top side of the ball, and then gets deflected downward. For a breaking pitch, which is thrown with topspin, it's the opposite, so the air on the bottom of the ball is deflected upward. Gayley says that deflection then acts like a mini jet engine that can cause an acceleration that fights gravity for the fastball, causing the "hop,” or assists gravity for the breaking ball, causing the ball to dive or slide.
“You can think of it like the ball is trying to leave a vacuum in its wake, but nature abhors a vacuum, so either the air above or the air below has to move in to fill that vacuum,” Gayley says. “The spin of the ball controls whether that air fills in from the top, on a fastball, or from the bottom, on a curveball, and in moving down or up the air acts like a mini jet engine.”
But even with his doctorate in physics, Gayley suspects Shulista and other pitchers know more about breaking pitches as he does because of their experience.
“A good pitcher will know intuitively more than science can explain,” he says. “And solving equations won’t win the World Series.”