Ever wonder why baseball players tend to take a step forward on a fly ball even if the ball will undoubtedly (from our vantage point) go behind them?
It turns out that
something called Optical Acceleration Cancellation (OAC), used the acceleration of the ball through the vision field as a guide for player movement.
As a fielder watches the ball rise, he moves either forward or backwards so that the ball moves at a constant speed through his field of vision. If he moves too far forward, the ball will rise faster and may eventually fly over his head. If he takes too many steps back, the ball will appear to rise slower and will drop in front of him.
By managing the ball’s position with his movement, a fielder will end up at the right spot at the right time.