How the Physics of Baseball Works

Breaking Down the Swing, Millisecond by Millisecond

Facing a world-class pitcher might be one of the most intimidating prospects in all of sports. Consider the situation for a typical batter: He stands at home plate, awaiting the throw from the opposing pitcher, positioned just 60.5 feet (18.4 meters) away. A good fastball pitcher can hurl the ball at about 94 mph (151 kph). That means the ball covers the distance between the mound and home plate in 0.439 seconds, or 439 milliseconds.

To put that in context, remember that a voluntary blink of the eye requires 150 milliseconds. In a little less than three blinks, the batter must see the ball, judge its trajectory, decide whether to swing and then, potentially, swing. It's no wonder hitting safely just three out of 10 at-bats is considered good. Or, as Ted Williams once observed: "Baseball is the only field of endeavor where a man can succeed three times out of 10 and be considered a good performer."

Successful batters have two qualities you hear shouted every day at ball fields: "good eyes" and "quick hands." If we dissect a batter's reaction, millisecond by millisecond, this is what we get [source: Adair]:

The instant the ball leaves the pitcher's hand, light bounces from the leather surface and races to the batter's eye. There, it takes 75 milliseconds for the batter's eye to form a picture and send it to the brain: 25 milliseconds for the retina to process incoming data, 20 milliseconds for that data to travel to the brain and 30 milliseconds for the brain to construct an image out of the information. As the ball travels toward the plate, additional images arrive in the brain every 25 milliseconds, like frames in a motion picture.
The batter then has about 50 milliseconds for thinking. In this short time, his brain must analyze the pitch and select a suitable swing or decide that the pitch will land out of the strike zone.
Next, the batter's brain must send signals to the muscles of his legs, torso and arms. This manifests itself as electrochemical impulses originating in the cerebral cortex and then zipping along nerve fibers to the extremities. In all, it takes 25 milliseconds for the impulses to get from the brain to individual muscle fibers in the lower legs.
Finally, the muscles respond, but not instantly. A baseball swing requires a full 150 milliseconds to complete. This takes into account the time for muscles to contract, move their attached limbs and bring the bat around at a speed close to 80 mph (129 kph). That means a good batter is well into his swing when the ball is still about 18 feet (5 meters) from home plate. If he's 10 milliseconds too early or too late, he'll miss the ball completely.

That's all timing. What about the swing itself?