Air flow images The ball on top is smooth. The one on the bottom has a rough surface...

By varying grips, wrist spins, and pitching motions, the pitcher can make the ball curve, rise, drop, change speeds,or just plain GO FAST. Speed is the most important aspect of the pitcher's game, and "go fast" is what a hardball is designed to do. The raised red cotton stitching that holds the cowhide covering of the ball together serves more than just an ornamental function. Without it, the ball wouldn't travel as far or as fast. When the ball is airborne, the stitching disturbs the "boundary layer," the paper-thin layer of air closest to the surface of the ball. As the ball spins, some of this slightly turbulent air rotates with the ball.

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Jim Poole
  Jim Poole  

At high speeds, the airstream friction against this rotating turbulence is less than it would be against the actual surface of the ball. There is a drastic overall decrease in drag, making it possible for a major league "flame-thrower" to hurl the ball at speeds of 90 to 100 miles an hour. This leaves the batter with less than half a second to decide whether he will swing, hold up, or dive for cover. (This same "boundary layer" effect explains why a golf ball, which normally travels over 200 yards on a drive, would travel only 50 yards without its characteristic dimples.)

The best way for the pitcher to transfer the whip action of his wrist and arm into straight-ahead, no-nonsense velocity is to throw the ball overhand, with the index and middle fingers placed close together on the seams of the ball. Now, if the pitcher snaps the ball down and to the side as he releases it, thus giving it a spin, something altogether different results: a curveball.