What happens to the ball depends on what spin was put on it. This all has to do with the fact that there is drag force, or air resistance. A curve ball is created when a ball is spinning. The faster flowing air under the ball creates less pressure, which forces the ball to dive or break. Baseball would be a dull game without drag force because there would be no curves, sliders, or knuckle balls. So how exactly do pitchers throw the curve balls? The pitcher holds onto the ball with his middle and index fingers on or next to the stitching on the ball and they place their thumb directly beneath. As they throw the ball, they snap their wrist in a turning motion, like turning a door knob, to make the ball spin in the direction of the throw. The stitching on the ball as well as the rotation of the ball, causes higher air pressure on one side of the ball. The higher velocity difference puts more stress on the air flowing around the bottom of the ball. The stress causes the air to break away from the balls surface sooner. Conversely, the air at the top of the spinning ball, subject to less stress due to the lower velocity difference and can hang onto the ball's surface longer before breaking away. Therefore curveballs do most of their curving in the last quarter of their trip.