Robert Calvin "Cal" Hubbard was a pioneering American athlete who achieved extraordinary success in two major professional sports. As an offensive tackle in the National Football League, he played for the New York Giants and Green Bay Packers, winning four NFL championships. After his football career, he became a highly respected umpire in Major League Baseball's American League for 16 seasons. Hubbard holds the unique distinction of being the only person inducted into both the Pro Football Hall of Fame and the National Baseball Hall of Fame.