Discover: How a knuckleball baffles baseball hitters – and physicists

From Andrew Grant at Discover Magazine on November 14, 2012, with mention of SABR member Alan Nathan:

Later on today Major League Baseball will announce the winners of the Cy Young Award, given to the year’s best pitchers in the American and National leagues. The frontrunner in the National League is New York Mets pitcher R.A. Dickey. If he wins, it would be remarkable, and not just because he is a relatively ancient 38 years old or because he plays for the perennial punch line Mets. Dickey would become the first Cy Young winner whose repertoire consists primarily of the knuckleball, a baffling pitch whose intricacies scientists are only now beginning to understand.

Most pitchers, including the other Cy Young finalists, try to overwhelm hitters with a combination of speed and movement. They throw the ball hard—the average major league fastball zooms in at around 91 miles per hour—and generate spin (up to 50 rotations a second) that makes the ball break, or deviate from a straight-line trajectory. Dickey does neither of those things. Rather than cock his arm back and fire, he pushes the ball like a dart so that it floats toward the plate between 55 and 80 mph. The ball barely spins at all—perhaps a quarter- or half-turn before reaching the hitter.

 That lack of rotation turns out to be the reason Dickey can get away with throwing the pitch more than 85 percent of the time. A baseball is not perfectly smooth—it has stitches that rise about seven-hundredths of an inch above the skin of the ball. When a typical pitcher throws, the ball spins so quickly that those stitches become irrelevant; it moves through the air as if it were perfectly round. But when the ball barely rotates, that slight protrusion becomes very important. The seams create turbulence as they cut through the air, leading to forces that can push the ball in any direction. “The movement is all over the place,” says Alan Nathan, a physicist at the University of Illinois at Urbana-Champaign who studies the physics of baseball. “It’s the only pitch that’s as likely to go up as down and as likely to go left as right.”

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Originally published: November 14, 2012. Last Updated: November 14, 2012.