The oldest football clubs trace their origins to the mid-19th century, a period when footballevolved from being a casual pastime to an organised, mainstream sport.
The identity of the oldest football clubs in the world, or even in a particular country, is often disputed or claimed by several clubs, across several codes of football. Late[clarification needed]rugby clubs also referred to themselves, or continue to refer to themselves, as simply a "football club", or as a "rugby football club". "Club" has always meant an independent entity and, during the historical period in question, very few high school or university teams were independent of the educational institutions concerned. Consequently, school and university football teams were seldom referred to as "clubs". That has always been the case, for example, in American football, which has always had ties to college sport in general. Conversely, however, the oldest still-existing "football club" with a well-documented, continuous history is Dublin University Football Club, a rugby union club founded in 1854 at Trinity College, Dublin, Ireland, although there exists some record of Guy's Hospital Football Club being founded in 1843.