Baseball is a sport with a long history of superstition. From the very famous Curse of the Bambino to some players' refusal to wash their clothes or bodies after a win, superstition is present in all parts of baseball. Many baseball players—batters, pitchers, and fielders alike— perform elaborate, repetitive routines prior to pitches and at bats due to superstition. The desire to keep a number they have been successful with is strong in baseball. In fact anything that happens prior to something good or bad in baseball can give birth to a new superstition. Some players rely on a level of meta-superstition: by believing in superstitions they can focus their mind to perform better. Many players and fans also believe that superstitions propagate their own fulfillment by influencing players and fans.
Some of the more common superstition include purposely stepping on or avoiding stepping on the foul line when taking the field, and not talking about a no-hitter or perfect game while it is in progress, a superstition that also holds for fans and announcers. Others include routines such as eating only chicken before a game like Wade Boggs, tapping the bat on the plate before an at bat, and drawing in the dirt in the batter's box before an at bat.
For further reading, see George Gmelch's analysis of the role of superstition in baseball.[1]