Fantasy football is an interactive competition in which people manage professional football players versus one another as general managers of a pseudo-football team. The players that an individual is able to manage are professional American football players in the National Football League.
The different actions people are able to make are drafting, trading, adding/dropping players, and changing rosters. Due to the growth of the Internet, fantasy football has increased in popularity.
http://en.wikipedia.org/wiki/Fantasy_football_(American)