XKCD has started explaining “what-if” scenarios with hard physics. In the first edition, XKCD answers the question “What would happen if you tried to hit a baseball pitched at 90% the speed of light?”. The explanation is straight, which only adds to how hilarious it is:
These gamma rays and debris expand outward in a bubble centered on the pitcher’s mound. They start to tear apart the molecules in the air, ripping the electrons from the nuclei and turning the air in the stadium into an expanding bubble of incandescent plasma. The wall of this bubble approaches the batter at about the speed of light—only slightly ahead of the ball itself.