Mr. Wizard at Bat

Mr. Wizard at Bat

It's no mystery why hitting major league pitching is so difficult; science reveals that the spin of the ball determines its trajectory.

Read Time:
3m 18sec

“Predicting a Baseball’s Path” by A. Terry Bahill, David G. Baldwin, and Jayendran Venkateswaran, in American Scientist (May–June 2005), P.O. Box 13975, 3106 East N.C. Hwy. 54, Research Triangle Park, N.C. 27709–3975.

When the innings stretch lazily through a warm afternoon and the crowd’s murmurings merge into a locustlike drone, baseball seems the perfect summer game. The field itself, however, is an arena of precise violence. Standing 60.5 feet from the batter, the pitcher hurls a ball just under three inches in diameter at a target only 17 inches wide. The ball arrives in less than half a second, sometimes dropping nearly six feet on its way to the plate.

The batter has perhaps one-seventh of a second to determine the ball’s speed and spin, another seventh of a second to decide whether—and where and when—to swing, and a fraction more to muscle the bat.

Science has more to offer the beleaguered man at the plate than illegal steroids, according to Bahill, a professor of systems engineering and computer science at the University of Arizona, and his colleagues, Baldwin, a former major-league pitcher, and Venkate­swaran, a graduate student.  

The batter can first pick up a few clues from the pitcher’s delivery. “To go through the strike zone, a 95-mile-per-hour fastball must be launched downward at a two-degree angle, whereas a 60-mile-per-hour change-up must be launched upward at a two-degree angle.” A major-league batter can often tell the difference.

The batter can also observe the pitcher’s hold on the ball as he releases it. “If a pitcher throws a curve ball and a batter has keen eyesight, he might be able to see the index and middle fingers roll across the face of the ball as the pitcher snaps it off.”

But the batter’s best source of information is the way the ball spins immediately after its release. Each type of pitch has its own spin, and detecting it requires excellent “dynamic visual acuity,” that is, the ability to perceive moving objects. For instance, Ted Williams, the great Boston Red Sox slugger, could read the label on a spinning 78-rpm record.

How the pitch appears to the batter depends on the pitcher’s grip. If the pitcher clutches the ball across the seams, it appears that four seams pass in front as the ball makes a revolution; if he holds the ball along the seams, it appears that only two seams do. To see what actually happens in flight, the authors skewered some baseballs on an electric drill and spun them at a fastball’s typical rate (1,200 rpm). The four-seam fastball was a gray blur with thin vertical red lines a seventh of an inch apart. The two-seam fastball showed two big red stripes, each about three-eighths of an inch wide, which made the spin direction more easily detectable.

The “flicker factor” also plays a role in detection, the authors speculate. The seams on the two-seam fastball appear almost as one, so as the ball rotates, it may flicker like a rapidly blinking light. That flickering could reveal if the ball has topspin (a curve ball) or backspin (a fastball). There’s no flicker with a four-seam pitch, though, since the “blinking” of the four individual seams is so rapid.

Unfortunately for batters, most pitching coaches recommend a four-seam grip for the fastball. But pitchers generally use the same grip for the fastball and the slider (a pitch that travels faster than a curve ball but spins less) to avoid tipping off the pitch. On the slider, the four-seam grip works to the batter’s advantage because it produces the perception of a red dot on the ball visible from home plate. Eight of 15 former major leaguers Bahill and his colleagues surveyed recalled seeing just such a dot. A smart pitcher could use the two-seam grip to avoid this telltale signal. Now if only future Babe Ruths could keep this scientific knowledge out of the hands of pitchers!

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