Myth of the Rising Fasball

Peter J. Brancazio
Professor Emeritus of Physics
Brooklyn College, The City University of New York

Pitchers, batters and catchers swear that a ball can rise at the plate.

Illustration by Danilo Ducak

Years ago, baseball players and fans commonly believed that it was possible to throw a rising fastball--a pitch that would curve upward or hop as it approached the batter. This could be done, it was thought, by gripping the baseball across the seams and releasing the pitch with a wrist snap that would impart a pronounced backspin on the ball. Although they could not explain why it happened, pitchers, batters and catchers were convinced that if the pitch were thrown at high speed--over 90 mph--it would rise as it crossed the plate, causing the batter to misjudge the trajectory and swing under the ball. They were certain the ball rose because they could see it rise.

As a longtime baseball fan and a physicist specializing in the physics of sports, I was curious to find out whether the rising fastball was for real. After all, a baseball must obey the laws of physics, and there was a well-established theory and sufficient data available to allow me to calculate the aerodynamic forces on a baseball in flight. The basic principles are relatively simple. After the ball leaves the pitcher's hand, it is subject to just three forces: gravity (equal to the weight of the ball) pulling it vertically downward; aerodynamic drag, created by the collision of the ball with the surrounding air, which reduces its forward speed; and what is known as the Magnus force, generated by the interaction of the spinning surface of the ball with the air. The ball generates a low-pressure wake behind it as it moves through the air, but if the surface is spinning, the wake is deflected sideways. According to Newton's law of action and reaction, if the ball deflects the air to one side, the air will push the ball in the opposite direction. The Magnus force always acts perpendicular to the path of the ball, deflecting it sideways according to the direction of spin. It is this force that allows pitchers to throw a repertoire of breaking balls--curveballs, sliders, sinkers, etc.--by adjusting the rate and direction of the spin on the ball along with the speed and location of the pitch. To throw a rising fastball, the Magnus force must be directed upward, opposing the pull of gravity, and this can be achieved by throwing the ball with backspin. If the Magnus force is greater than the weight of the ball, then the net force on the ball will cause it to rise.

When I ran computer simulations of pitches, I made some interesting discoveries. I learned that over the standard pitching distance of 60 ft. 6 in., a ball loses about 9 percent of its initial speed due to aerodynamic drag--thus a pitch launched at 90 mph will have slowed to 81 mph when it reaches the batter. The pitch takes only about 0.44 second to cover the distance. During this interval the ball falls about 3 ft. due to the pull of gravity. A batter has less than half a second to judge the trajectory of the ball, decide whether to swing, and then bring his bat around to the projected point of contact. Hitting a baseball at the major league level, I discovered, is a truly remarkable feat.

Most significantly, I discovered that in order for the ball to truly rise in flight--for the Magnus force to exceed the weight of the ball--the pitch would have to be launched with a backspin of more than 3600 rpm. This is far beyond the capacity of any major league pitcher. High-speed photography shows that spin rates of about 1800 rpm are the best that can be achieved. Thus, it is not humanly possible to throw a true rising fastball. With the ball spinning at 1800 rpm and traveling at 90 mph, the Magnus force retards the vertical drop by a little more than a foot. Instead of dropping 3 ft. vertically on its way to the plate, the ball drops slightly less than 2 ft. I concluded that the rising fastball is an optical illusion. The ball appears to rise only because it doesn't fall as much as the batter expects it to--in other words, the ball rises only in relation to the batter's expectations.

Over time, a number of other scientists have verified my results. The most convincing confirmation has come from real-time tracking of baseball pitches using multiple video cameras and rapid computerized reconstruction of the trajectories. To the best of my knowledge, no one has ever recorded a fastball rising as it crosses the plate. A Google search on the term "rising fastball" reveals dozens of articles all attesting to the fact that the rising fastball is an optical illusion. To the exquisitely trained eyes of a top-flight batter or catcher, the ball appears to rise because it does not fall as much as it would without the backspin.

Myth of the Rising Fasball. PopularMechanics.Com (2005). Retrieved December 4, 2005, from PopularMechanics.com: http://www.popularmechanics.com/science/sports/1283281.html