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Why hitting curveballs scores more homers

With Memorial Day upon us, scientists' thoughts turn to summer sports, and what could be more summer-y than Frisbee and baseball?
/ Source: The Associated Press

With Memorial Day upon us, scientists' thoughts turn to summer sports, and what could be more summer-y than Frisbee and baseball?

Conventional wisdom in baseball holds that, everything else (such as the speed of the bat and how solidly it connects) being equal, a fastball is more likely to be smacked for a home run than a curveball is. But when University of California, Davis, engineering professor Mont Hubbard and his colleagues modeled all the forces on a batted ball, they found that, in baseball as in politics, it's the spin that matters _ and conventional wisdom, in this case at least, is wrong.

When a curveball leaves the pitcher's fingers it has topspin, which means the top of the ball rotates in the direction of flight (toward the plate). Fastballs, in contrast, have backspin, with the bottom of the ball rotating in the direction of flight. Topspin causes a ball to experience a downward force, because the rotation changes the distribution of air pressure around the ball so there is more pressing down on the ball than up. Hence curveballs' habit of suddenly plunging, to batters' dismay. Backspin, in contrast, generates an upward force, somewhat like the one that keeps an airplane aloft, which is why a fastball rises unless the pitcher gives it a countervailing spin.

When the bat makes contact, the most obvious thing it does is reverse the ball's direction, so it heads toward the field rather than the plate. But contact also changes the ball's spin. Assuming good contact in each case, a fastball that arrived with backspin therefore leaves with topspin, while a curveball arriving with topspin leaves with additional backspin and thus more home run potential.

"A curveball already has batted backspin," says Prof. Hubbard. "With a fastball, in order to give it backspin and let it benefit from aerodynamics, you have to reverse the spin," which is tough to do. The well-hit curveball heads for the field with more of the kind of spin that gives it fence-clearing lift and distance.

Once the ball is headed for the outfield, players have to perform complex geometric calculations to reach the right spot at the right time. But maybe it's not that tough: Scientists have found that dogs perform the exact same calculation when catching Frisbees.

In 1995, scientists found that outfielders manage to wind up where and when the ball does by running along a curving path. This is harder to describe than it is to execute, but basically, for anything other than a ball coming straight at you, the idea is to run so that from your viewpoint the ball seems to follow a straight line, upward, until you catch it.

If this seems impossible _ the ball, after all, starts falling to the ground after it peaks _ consider that if you keep tilting your head back a falling object seems to hang in the air. Similarly, if the fielder takes the correct curving path toward a ball, it seems to fly along a straight, rising line in front of him until its trajectory intersects his own. We call that a catch.

In a paper to be published in the July issue of Psychological Science, researchers describe a study in which they fitted micro-video-cameras to the heads of Romeo, a springer spaniel, and Lilly, a border collie. The cameras faced outward, to capture what the dogs saw.

The team, led by Dennis Shaffer of Ohio State University, Mansfield, found that dogs shagging Frisbees follow the same kind of path as outfielders. As soon as a Frisbee was launched, Romeo and Lilly ran a path that made it appear to fly along a straight, rising line, finally grabbing it with their mouth. "This seems to be a universal strategy related to predatory and mating behavior," says Prof. Shaffer, "maybe evolving from the same mechanisms used by male flies to intercept females in midair."

In January, I described a study concluding that the reason there are more hit batsmen in the American League than the National League (15 percent more since the AL adopted the designated hitter rule in 1973) isn't that the DH puts one more strong, aggressive hitter into the lineup. (Hurlers are likely to pitch inside to strong hitters; too inside and the batter is hit.) Instead, AL pitchers, who never bat, don't risk retaliation for plunking opposing batters.

Just in case any fans still retain their naivete on this, Hank Allessio of Walden Consultants Ltd., Hopkintown, Mass., analyzed what he calls "intent to intimidate." He graphed walks allowed (a measure of wildness) against hit batsmen per nine innings, using career stats through the 2003 season. Many top pitchers, including Randy Johnson and Roger Clemens and Bob Gibson, fall roughly in the middle, issuing three to four walks and plunking one batter every three games or so.

But some pitchers with excellent control hit a batter almost twice as often. The pitcher with the most extreme walks-to-plunks record: Red Sox ace Pedro Martinez. Coincidence? Mr. Allessio, a self-described "Yankees fan in eastern Massachusetts," thinks not. After Martinez moved from the NL to Boston in 1998 and no longer needed to worry about being the victim of retaliation, his control improved but his rate of hit batsmen rose.

Readers may draw their own conclusion.