In baseball, the umpire is the person charged with officiating the game, including beginning and ending the game, enforcing the rules of the game and the grounds, making judgment calls on plays, and meting out discipline. The term is often shortened to the colloquial form ump. They are also addressed as blue due to the colour of the uniform some umpires wear. (On the professional level, umpires generally disdain being called "blue", preferring instead to be called by their name; especially considering the fact that MLB umpires no longer wear blue) Although games were often officiated by a sole umpire in the formative years of the sport, from the turn of the 20th century onward officiating has been commonly divided among several umpires, who form the umpiring crew.