What is curveball

With a snap of the wrist, the pitcher lets fly the ball.
It rises and then, as it nears the plate, sinks into the strike zone.
One of the baseball's most thrilling moves, the curveball can be explained by differences in air pressure over and under the ball.
Its topspin means the top part of the ball spins in the direction of pitch --- and against the air.
This causes greater friction (enhanced by the baseball's traditional stitching) than occurs under the ball, which spins with the airflow.
Thus, air flows faster over the bottom of the ball, creating a low-pressure area compared with the air on top.
The higher-pressure air pushes the ball down.