According to the National Football League, the 1972 Miami Dolphins are the only undefeated, untied Super Bowl champions. But pro football''s first undefeated championship team was crowned in 1948, when the Cleveland Browns won their third straight All-America Football Conference title with a record of 15 victories, no losses and no ties. They were led by Hall of Fame head coach Paul Brown, whose methods revolutionized the game and influenced every coach who followed. On the field, the ''48 Browns'' roster featured six future Hall of Famers, including Marion Motley and Bill Willis, who broke pro football''s color barrier with the first snap of the 1946 season.