Shagging Flies isn't all that Easy

Fall is in the air all around us! To us baseball fanatics, that means the World Series. Sadly (to me), like Lucy in Charles Schultz's Peanuts strip, I was never much of an outfielder.

But we've got our excuses. Catching a fly ball is not the easiest thing in the world. Trying to figure out where to be on the field when the ball comes down could drive even the most sophisticated computer into endless loops. But good outfielders do it seemingly without effort. How?

Peter Brancazio, as he reported in an old issue of Science Digest, thinks he has it down. It's not just the eyes--it's the inner ear, the sensory apparatus used to maintain balance, distinguish up from down and detect acceleration.

Try this: hold up one finger in front of your face and focus your gaze on it. Now turn your head rapidly from side to side, keeping your eyes on your finger. Stays focused and in place, doesn't it? But now keep your head steady and move your finger from side to side at the same rate as before and try to keep it in focus by following it with your eyes.

The fact that you could keep your finger in focus in the first test but not in the second demonstrates that the inner ear signals are processed more rapidly by the brain than visual signals.

But what has this to do with judging where a fly ball will land? Brancazio thinks that the reaction of an experienced outfielder is to move his head to track the ball, rather than his eyes.

There's more to it than that, though. A batted ball doesn't follow a perfect parabolic arc, as it would in a vacuum. The outfielder must also mentally calculate just how much a ball is going to be slowed down by aerodynamic drag before it drops. In Mexico City, this would be significantly less than it would be in the Alaska League. Ballplayers learn this only through experience.

The difference is significant. Consider a raindrop falling from 10,000 feet. In a vacuum, it would arrive at the ground with a velocity in excess of 565 miles per hour. That's positively lethal, but in the actual situation, the small size and weight of a raindrop and the presence of the atmosphere limit its terminal velocity to only about 15 miles per hour. The terminal speed of a baseball (regardless of how high it is when it's dropped) is about 95 miles per hour, which is only slightly less than its velocity when hit off a home-run swing.

Catching a fly ball in a high wind at an arbitrary elevation is something at which the computer still cannot match the skill of a human athlete--but then, neither can I.