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Predicting a Baseball's Path

A batter watches the pitcher's motion plus the spin on the ball to calculate when and where it will cross the plate

A. Terry Bahill, David Baldwin, Jayendran Venkateswaran

Figure 1. As a professional pitcher releases a baseball...Click to Enlarge Image

Imagine being at the center of the most dramatic moment in baseball. It's the bottom of the ninth inning of the seventh game of the World Series—two outs, the tying run on second, the winning run on first, and you are the batter. Everything depends on you. The trouble is: The most fearsome pitcher in baseball stands on the mound. He has an awesome assortment of pitches: fastball, change-up, curveball, slider and knuckleball. You want any advantage that you can get in predicting where each pitch will go.

With the crowd going wild and sweat pouring from your every pore, you have to concentrate on the ball that is about to be launched in your direction. You must gather as much information about the pitch as quickly as you can in order to make crucial decisions.

As we will show, you get just a few hundreds of milliseconds to figure out what kind of pitch—perhaps traveling at almost 100 miles per hour—is heading toward the plate. In that instant, you must observe the ball's spin and predict how it will move on its way to the plate. It's a daunting computational task. Luckily, we can describe a few clues for you to use. And you will need them soon, because that fearsome pitcher is rocking back on his pivot leg. In a split second, his arm will swing through a great arc and send a baseball hurtling your way.

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