Etymology
There is some confusion as to the origin of the word fan. Paul Dickson, in his Dickson Baseball Dictionary, cites William Henry Nugent's work that traces it to fancy, a 19th century term from England that referred mainly to followers of boxing. It was originally shortened to fance then just to the homonym fans. The word emerged as an Americanism around 1889. Many assume that it's a shortened version of the word fanatic, and the word did first become popular in reference to an enthusiastic follower of a baseball team. (Fanatic itself, introduced into English around 1525, means "insane person". It comes from the Modern Latin fanaticus, meaning "insanely but divinely inspired". The word originally pertained to a temple or sacred place [Latin fanum, poetic English fane]. The modern sense of "extremely zealous" dates from around 1647; the use of fanatic as a noun dates from 1650.) However, the term "fancy" for an intense liking of something, while being of a different etymology, coincidentally carries somewhat the same connotation as "fanatic".