With the crack of the bat, the ball sails deep into the outfield. The center-fielder starts his run, moving back and to the right, trying to keep his eyes on the ball. His pace quickens initially, then slows down as the ball approaches. He arrives just in time to make the catch.
How did he know where to run and at what speed so that he and the ball intersected at the same exact spot on the field? Why didn't he sprint to the landing spot and then wait for the ball to drop, instead of running at a controlled speed to arrive just when the ball did?
Fielding requires extensive coordination of the eyes, brain and body. There are two leading theories of how we do it.
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LOT theory
Linear Optical Trajectory (LOT) says a fielder adjusts his movement so that the ball's trajectory follows a straight line through his field of vision . LOT was developed by Michael McBeath, associate professor of psychology at Arizona State University.
According to LOT theory, a fielder uses the information provided by the path of the ball to constantly adjust his path, so that he intersects with it at the right time and place, rather than computing the landing point of the ball, which would have the fielder racing to that spot and waiting.
OAC theory
LOT theory evolved from an earlier theory called Optical Acceleration Cancellation (OAC), which was originally proposed by the late Seville Chapman, a physicist at Stanford University. OAC includes the same ideas as LOT, but only explains the fielder's movements in one direction.
According to OAC, fielders move backward and forward to keep the ball within a certain part of their field of vision at about a 45 degree angle above the ground.
For example, if a fielder was to stand still, and the ball was to land behind him, his eyes would track the ball all the way up to directly over his head -- a 90 degree angle. If the ball landed in front of him at 0 degrees -- he would see the ball rise and fall, but his viewing angle may not rise above 45 degrees.
LOT and OAC argue that the fielder repositions himself throughout the flight of the ball in order to keep his viewing angle between 0 and 90 degrees. If the ball rises too fast, he moves backward. If the viewing angle is low, then the fielder moves forward. He can't always make to the landing spot in time, but keeping the ball at about a 45 degree angle by moving back and forth will help ensure that he arrives at the right place.
While OAC explains what happens when a ball is hit directly at a fielder, LOT helps add the side-to-side dimension, as in the example of a ball hit to the right of the fielder.
Now, the next time your favorite outfielder takes two steps in, only to have the ball sail over his head , you'll have some idea of what went wrong.
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Dan Peterson writes about sports science at Sports Are 80 Percent Mental.
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