The CFL was officially named on January 19, 1958,[4] upon the merger between the Interprovincial Rugby Football Union or "Big Four" (founded in 1907) and the Western Interprovincial Football Union (founded in 1936).[5] Before the introduction of interlocking play in 1961, Eastern teams competed against Western teams only in pre-season and the Grey Cup Championship (similar to Major League Baseball in the United States prior to the 1997 season).