The ball is moving so fast, everything else is stationary relative to it, including the molecules in the air, and the atoms in the air molecules actually fuse with the atoms in the ball’s surface. Each collision releases a burst of gamma rays and scattered particles. The gamma rays and particles expand in a bubble of incandescent plasma.
The ball reaches the plate in about 70 nanoseconds, although most of the ball is actually gone by that point, and it is academic from the batter's perspective since he has just realized the pitch has been thrown because it is moving at almost the speed of light.
The plasma cloud hits the bat, batter, catcher, umpire and backstop at the same time, hurling them backwards as they disintegrate and then engulfs the dugouts, stands, stadium and neighborhood in a massive fireball.
The XKCD analysis concludes:
"A careful reading of official Major League Baseball Rule 6.08(b) suggests that in this situation, the batter would be considered "hit by pitch", and would be eligible to advance to first base."The details are kinda technical and can be found here.