NFL

On August 20, 1920, a meeting was held by representatives of the Akron Pros, Canton Bulldogs, Cleveland Indians, and Dayton Triangles at the Jordan and Hupmobile auto showroom in Canton, Ohio. This meeting resulted in the formation of the American Professional Football Conference (APFC), a group who, according to the Canton Evening Repository, intended to "raise the standard of professional football in every way possible, to eliminate bidding for players between rival clubs and to secure cooperation in the formation of schedules".

A second meeting was held on September 17, 1920, with representatives from teams within four states: Akron, Canton, Cleveland, and Dayton from Ohio; the Hammond Pros and Muncie Flyers from Indiana; the Rochester Jeffersons from New York; and the Rock Island Independents, Decatur Staleys, and Racine (Chicago) Cardinals from Illinois. The league was renamed to the American Professional Football Association (APFA). The league elected Jim Thorpe as its first president, and consisted of 14 teams (the Buffalo All-Americans, Chicago Tigers, Columbus Panhandles and Detroit Heralds joined the league during the year). The Massillon Tigers from Massillon, Ohio was also at the September 17 meeting, but did not field a team in 1920. Only two of these teams, the Decatur Staleys (now the Chicago Bears) and the Chicago Cardinals (now the Arizona Cardinals), remain in the NFL.

Although the league did not maintain official standings for its 1920 inaugural season and teams played schedules that included non-league opponents, the APFA awarded the Akron Pros the championship by virtue of their 8–0–3 record. The first event occurred on September 26, 1920, when the Rock Island Independents defeated the non-league St. Paul Ideals 48–0 at Douglas Park. On October 3, 1920, the first full week of league play occurred. The following season resulted in the Chicago Staleys controversially winning the title over the Buffalo All-Americans. On June 24, 1922, the APFA changed its name to the National Football League (NFL).

In 1932, the season ended with the Chicago Bears (6–1–6) and the Portsmouth Spartans (6–1–4) tied for first in the league standings. At the time, teams were ranked on a single table and the team with the highest winning percentage (not including ties, which were not counted towards the standings) at the end of the season was declared the champion; the only tiebreaker was that in the event of a tie if two teams played twice in a season, the result of the second game determined the title (the source of the 1921 controversy). This method had been used since the league's creation in 1920, but no situation had been encountered where two teams were tied for first. The league quickly determined that a playoff game between Chicago and Portsmouth was needed to decide the league's champion. The teams were originally scheduled to play the playoff game, officially a regular-season game that would count towards the regular season standings, at Wrigley Field in Chicago, but a combination of heavy snow and extreme cold forced the game to be moved indoors to Chicago Stadium, which did not have a regulation-size football field. Playing with altered rules to accommodate the smaller playing field, the Bears won the game 9–0 and thus won the championship. Fan interest in the de facto championship game led the NFL, beginning in 1933, to split into two divisions with a championship game to be played between the division champions. The 1934 season also marked the first of twelve seasons in which African Americans were absent from the league. The de facto ban was rescinded in 1946, following public pressure and coinciding with the removal of a similar ban in Major League Baseball.

The NFL was always the largest professional football league in the United States; it nevertheless faced numerous rival professional leagues through the 1930s and 1940s. Rival leagues included at least three separate American Football Leagues and the All-America Football Conference (AAFC), on top of various regional leagues of varying caliber. Three NFL teams trace their histories to these rival leagues; the Los Angeles Rams who came from a 1936 iteration of the American Football League, and the Cleveland Browns and San Francisco 49ers, both from the AAFC. By the 1950s, the NFL had an effective monopoly on professional football in the United States; its only competition in North America was the professional Canadian football circuit, which formally became the Canadian Football League (CFL) in 1958. With Canadian football being a different football code than the American game, the CFL established a niche market in Canada and still survives as an independent league.

A new professional league, the fourth American Football League (AFL), began to play in 1960. The upstart AFL began to challenge the established NFL in popularity, gaining lucrative television contracts and engaging in a bidding war with the NFL for free agents and draft picks. The two leagues announced a merger on June 8, 1966, to take full effect in 1970. In the meantime, the leagues would hold a common draft and championship game. The game, the Super Bowl, was held four times before the merger, with the NFL winning Super Bowl I and Super Bowl II, and the AFL winning Super Bowl III and Super Bowl IV. After the league merged, it was reorganized into two conferences: the National Football Conference (NFC), consisting of most of the pre-merger NFL teams, and the American Football Conference (AFC), consisting of all of the AFL teams as well as three pre-merger NFL teams.

Today, the NFL is the most popular sports league in North America – with much of the league's growth and popularity attributable to former Commissioner Pete Rozelle, who led the league from 1960 to 1989. Overall annual attendance increased from 3 million at the beginning of his tenure to 17 million by the end of his tenure, and 400 million global viewers watched 1989's Super Bowl XXIII. The NFL established NFL Properties in 1963. The league's licensing wing, NFL Properties, earns the league billions of dollars annually; Rozelle's tenure also marked the creation of NFL Charities and a national partnership with United Way. Paul Tagliabue was elected as commissioner to succeed Rozelle; his 17-year tenure, which ended in 2006, was marked by large increases in television contracts and the addition of four expansion teams, as well as the introduction of league initiatives to increase the number of minorities in league and team management roles. The league's current Commissioner, Roger Goodell, has focused on reducing the number of illegal hits and making the sport safer, mainly through fining or suspending players who break rules. These actions are among many the NFL is taking to reduce concussions and improve player safety. Prior to 2021, the NFL had utilized race-based adjustments of dementia claims in the $1 billion settlement of concussion claims, which had been criticized by critics before the NFL decided to end what was called "race-norming". On May 21, 2024, the NFL announced the NFL Source initiative, aimed at increasing the number of minority- and women-owned businesses that work with the league throughout the year. NFL Source will be mandatory for teams that host major events, such as the Super Bowl and the NFL Draft, and their organizing committees, but will be optional for other contracts at the team level. The NFL will partner with the U.S. Black Chambers, Inc to help local businesses across the country obtain the certifications necessary to do business with the league in furtherance of its efforts to increase partnerships with certified and underrepresented businesses that are 51% owned and operated or led by a veteran, woman, minority, person with disabilities or LGBTQ+. In 2015, a class-action lawsuit was filed on behalf of NFL Sunday Ticket subscribers, alleging that the NFL, its member teams, its broadcast partners, and DirecTV engaged in a conspiracy to violate antitrust law, by granting DirecTV exclusive rights to sell the Sunday Ticket product, thereby restricting competition and forcing viewers to pay super competitive prices to view out-of-market games. On June 27, 2024, a jury in Los Angeles found that the NFL had violated antitrust law in setting the price of the Sunday ticket package and ordered a penalty totaling more than $4.7 billion. With triple damages allowed under federal antitrust laws, the NFL could ultimately be liable for $14.39 billion. The league said it would ask the judge to set the verdict aside then appeal the verdict if needed.

From 1920 to 1934, the NFL did not have a set number of games for teams to play, instead setting a minimum. The league mandated a twelve-game regular season for each team beginning in 1935, later shortening this to eleven games in 1937 and ten games in 1943, mainly due to World War II. After the war ended, the number of games returned to eleven games in 1946, and later back to twelve in 1947. The NFL went to a 14-game schedule in 1961, which it retained until switching to a 16-game schedule in 1978. In March 2021, the NFL officially adopted a 17-game schedule after gaining the agreement of the National Football League Players Association (NFLPA).

Having an odd number of games in the schedule will give half the teams nine games as the home team, while half the teams have only eight home games. To minimize the perceived benefit on competition of having more home games, the extra home game will be rotated between the two conferences each year. This is because playoff berths are allocated at the conference level, so all teams within the conference will have played the same number of home games.

The NFL operated in a two-conference system from 1933 to 1966, where the champions of each conference would meet in the NFL Championship Game. If two teams tied for the conference lead, they would meet in a one-game playoff to determine the conference champion. In 1967, the NFL expanded from 15 teams to 16 teams. Instead of just evening out the conferences by adding the expansion New Orleans Saints to the seven-member Western Conference, the NFL realigned the conferences and split each into two four-team divisions. The four division champions would meet in the NFL playoffs, a two-round playoff. The NFL also operated the Playoff Bowl (officially the Bert Bell Benefit Bowl) from 1960 to 1969. Effectively, a third-place game, pitting the two conference runners-up against each other, the league considers Playoff Bowls to have been exhibitions rather than playoff games. The league discontinued the Playoff Bowl in 1970 due to its perception as a game for losers.

Following the addition of the former AFL teams into the NFL in 1970, the NFL split into two conferences with three divisions each. The expanded league, now with twenty-six teams, would also feature an expanded eight-team playoff, the participants being the three division champions from each conference as well as one 'wild card' team (the team with the best win percentage that did not win its division) from each conference. In 1978, the league added a second wild card team from each conference, bringing the total number of playoff teams to ten, and a further two wild card teams were added in 1990 to bring the total to twelve. When the NFL expanded to 32 teams in 2002, the league realigned, changing the division structure from three divisions in each conference to four divisions in each conference. As each division champion gets a playoff bid, the number of wild card teams from each conference dropped from three to two. The playoffs expanded again in 2020, adding two more wild card teams to bring the total to 14 playoff teams.