Professional American football championship games
Below is a list of professional football Championship Games in the United States, involving: 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), and the league was later renamed the National Football League (NFL). The NFL conducted play for thirteen years before creating a ""Championship Game"": from 1920 through 1932, league ""champions"" were determined by won-loss record with ties excluded, 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, while some played against college or semi-pro teams, some played "after" the season was over, and 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 also had no official Championship Games before it changed its name to the NFL in 1922. Boston/Washington Redskins owner George Preston Marshall, who credited with significant innovations by the NFL, convinced the NFL in 1933 to play  a Championship Game between the two Division winners following the success of the 1932 Playoff Game. Thus, 1933 was the year of the first national professional football Championship Game in the United States. See National Football League championships: note that game scores marked with a † (1921 and 1932) were "defacto" Championship Games, as these were the deciding games in determining a Championship, and also the last game played in that season - further, the Portsmouth Spartans, who were defeated in the 1932 Game, finished third as the Game counted in the season standings. 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 (i.e. the Championship Game of the 2011 NFL season was played in February 2012, but is listed here under 2011).