A fantasy sport (also known less commonly as rotisserie or roto) is a game, often played using the internet, where participants assemble imaginary or virtual teams composed of proxies of real players of a professional sport. These teams compete based on the statistical performance of those players in actual games. This performance is converted into points that are compiled and totaled according to a roster selected by each fantasy team's manager. These point systems can be simple enough to be manually calculated by a "league commissioner" who coordinates and manages the overall league, or points can be compiled and calculated using computers tracking actual results of the professional sport. In fantasy sports, as in real sports, team owners draft, trade, and cut (drop) players.

The history of fantasy games can be traced to the 19th century. The tabletop game Sebring Parlor Base Ball, introduced in 1866, allowed participants to simulate games by propelling a coin into slots on a wooden board. Later games featured outcomes determined by dice rolls or spinners. In 1930, Clifford Van Beek designed the board game National Pastime, which contained customized baseball cards of Major League Baseball (MLB) players. After rolling a pair of dice, participants would consult the card of the MLB player "at bat" to determine an outcome, which could range from a single, double, triple, or home run to a strikeout, putout, walk, or error. Players with better statistics in the previous season were more likely to receive favorable outcomes; this allowed National Pastime to become one of the first games to try to simulate the performances of real-life MLB players.

An example of such games was APBA, which was first released in 1951 and also contained cards of MLB players with in-game outcomes correlated to their stats from past seasons. Participants could compose fantasy teams from the cards and play against each other or recreate previous seasons using the statistics on the cards. Individual player cards and dice roll simulations were also emulated in the Strat-O-Matic game, which was first released in 1961. Daniel Okrent, who would later be credited with developing modern fantasy baseball, was an avid Strat-O-Matic player, telling Sports Illustrated in 2011 that "if there hadn't been Strat-O-Matic, I still think I would have come up with rotisserie, but unquestionably it helped."

In 1961, another early form of fantasy baseball was coded for the IBM 1620 computer by John Burgeson, then working for IBM. A user would select a team from a limited roster of retired players to play against a team randomly chosen by the computer. The computer would then use random number generation and player statistics to simulate a game's outcome and print a play-by-play description of it.

While some of these fantasy games produced outcomes based on the performances of real athletes, they were not designed to be played out over the course of a season, nor did they take current statistics into account, relying instead on those from previous years.

In the 1950s, Oakland, California businessman and future limited partner in the Oakland Raiders Wilfred "Bill" Winkenbach developed a fantasy golf game in which participants would select a roster of professional golfers and compare their scores at the end of a given tournament, with the lowest combined total of strokes winning. He also created a baseball game in which players drafted hitters and pitchers, comparing their real-life statistics against each other. These early experiments, however, failed to spread to the general public.

In 1960, sociologist William A. Gamson developed the Baseball Seminar league, in which participants would draft rosters of active MLB players and compare results at the end of the season based on the players' final batting averages, earned run averages, runs batted in, and win totals. Gamson would go on to play the game as a professor at the University of Michigan, where another competitor was Bob Sklar. One of Sklar's students was Daniel Okrent. According to Alan Schwarz's The Numbers Game: Baseball’s Lifelong Fascination with Statistics, Sklar told Okrent about the Baseball Seminar league.

Two years later, in a New York City hotel room during a 1962 Raiders cross-country trip, Winkenbach, along with Raiders public relations employee Bill Tunnel and Oakland Tribune reporter Scotty Stirling, developed the rules that would eventually be the basis of modern fantasy football. The inaugural league was called the Greater Oakland Professional Pigskin Prognosticators League (GOPPPL), and the first draft took place at Winkenbach's home in Oakland in August 1963. One of the league's original members, Andy Mousalimas, owned a sports bar in Oakland called the King's X, where the first public fantasy football league was founded in 1969. The idea spread by word of mouth when the patrons of other Bay Area bars visited the King's X for trivia contests.