and any interleague challenge games that included at least one champion of a major or borderline-major league.
Prior to 1920, no national professional football league existed, and play was scattered across semi-pro and professional leagues in the upper midwest. The first efforts at pro football championships were the World Series of Professional Football, featuring teams from and around New York City and the 1902 "National" Football League in Pennsylvania; two of the three "N"FL teams participated as one team in the World Series of Pro Football. The Ohio League and New York Pro Football League were two prominent regional associations in the 1910s (the NYPFL held an actual championship game in 1919). In 1920, teams from the Ohio League and New York Pro Football League, along with other midwestern teams, formalized into the American Professional Football Association (APFA); the league was later renamed the National Football League (NFL). The NFL conducted play for thirteen years before concocting a "championship game". From 1920 through 1932, league "champions" were determined by won-loss record, but the schedules and rules were so ill-defined that conflicts exist to this day over who the actual champions were. Some teams played more games than others; some played against college or semi-pro teams; some played after the season was over, some stopped play before a season was over. For example, in 1921, the Buffalo All-Americans disputed the Chicago Staleys' title, and in 1925, the Pottsville Maroons claimed the championship was theirs, not the Chicago Cardinals'.
The APFA had no championship games before it changed its name to the NFL in 1922. Boston/Washington Redskins owner George Preston Marshall is credited with significant innovations by the NFL. In 1933, Marshall convinced the NFL to play a championship game between two division winners. Thus, 1933 was the year of the first national professional football championship game in the United States. See National Football League championships.
Game scores marked with a † (1921 and 1932) were not official championship games, but were the deciding games in determining a championship and also the last games played in a season.
All games are listed under the year in which the majority of regular season games were played; especially since the 1960s, many championship games have been played in the January or, since 2002, February of the following year (for instance, the championship of the 2011 NFL season is played in February 2012, but will be listed in this list under 2011).
^Official championship game of the tournament, though historically considered unimportant. The game often considered to be the true championship of the series was when the Syracuse team defeated a combined Athletics-Phillies team known as "New York" by a score of 6-0.
^The Blues and Tigers had so many players in common that it was impossible to stage a championship between the two teams. The two teams were thus jointly given the title and merged operations the next year, with the Tigers name being spun off to another team.
^Buffalo-Phoenixville (the team, though having ostensibly different owners, was effectively the same team that played as Buffalo on Sundays and as Phoenixville on most Saturdays) petitioned the league for a share of the title, citing a greater win-loss differential with Akron and the fact that their lone loss was partially nullified under league rules by virtue of a later win against the same team. (The team played Akron under the Buffalo name; under the Buffalo name, the team was 9-1-1, under Phoenixville, 11-0-0.) However, Joseph Carr moved to give Akron the sole title, which was officially accepted in April 1921. The Decatur Staleys, at 10-1-2 and who also tied Akron 0-0 in their final game a week later, also petitioned for a share of the title.
^Post-season game that would have given title to Chicago Bears was struck down as illegal by league officers.