High Quality Content by WIKIPEDIA articles! In baseball, the uniform number is a number worn on the uniform of each player and coach. Numbers are used for the purpose of easily identifying each person on the field as no two people from the same team can wear the same number. Although designed for identification purposes only, numbers have become the source of superstition, emotional attachment, and honor (in the form of a number retirement). The number is always on the back of the jersey, often on the front, and occasionally seen on the left leg of the pants.