In the early 1900's, pitchers didn't specialize with a great slider, a 12-to-6 curveball, or a cut fastball. Nope, not even a knuckleball.
The most anticipated pitcher throw was the infamous "spitball." This pitch was the result of the pitcher spitting on the ball, which later became wiping sweat off the brow and on to the ball, which then became any moisture or substance on the ball used to loosen the friction between the pitcher's fingers and the ball.
The spitball would have unpredictable movement, which made it very difficult for batters to hit, but also made it very tough for a pitcher to control.
In 1920, rules were established to prevent the spitball, and the result was a strange set of rules just for pitchers on the mound.
Most basically put, a pitcher cannot lick his hand, wipe his brow, or adjust his waistline and then directly touch the ball.
The pitcher must first wipe his hand on the outside of his uniform and then proceed to grip the baseball.
This may seem like paranoia, since the spitball hasn't been widely practiced since the era it was banned in, but it is still a rule, and pitchers must abide.
Photo courtesy of Life Magazine