Really enjoyed this article from Sports Illustrated by Tom Verducci:
Hitting a baseball is hard enough on its most basic level. A 90-mph fastball will get to home plate in 400 milliseconds, but the hitter needs 200 of those to see the ball, send the image to the brain and process its speed, spin and location. The swing itself takes about 150 milliseconds—literally, the blink of an eye. That leaves a scant 50 milliseconds to decide whether to swing and, if so, on what path.
The goal is to connect a 2¼-inch-diameter bat barrel squarely with a three-inch-diameter baseball—without actually being able to see the ball right before contact. The eye can't follow an object moving that fast that close, so a hitter cannot track the pitch in its last five feet before it reaches the plate. Here's what that means: The batter loses sight of the baseball just when the pitcher wants the pitch to break off its path.