As part of their “What If?” series, Randall Munroe of xkcd and Henry Reich of MinutePhysics responded in detail to a viewer who asked what it would be like to hit a baseball going at 90% the speed of light.
The ball is going so fast that everything else is practically stationary. Even the molecules in the air are stationary. Air molecules vibrate back and forth at a few hundred miles per hour, but the ball is moving through them at 600 million miles per hour. This means that as far as the ball is concerned, they’re just hanging there, frozen.
According to Munroe and Reich, everything else that happens goes according to the nature of physics, although the scenario doesn’t look good for either the batter, the pitcher, or anyone else within the area.
When it reaches the batter, the center of the cloud is still moving at an appreciable fraction of the speed of light. It hits the bat first, but then the batter, plate, and catcher are all scooped up and carried backward through the backstop as they disintegrate. The shell of x-rays and superheated plasma expands outward and upward, swallowing the backstop, both teams, the stands, and the surrounding neighborhood—all in the first microsecond.