On August 9, 1976 — Cal Hubbard, with his induction to the Hall of Fame in Cooperstown as an umpire, becomes the first professional athlete to be elected into two Halls of Fame. In 1963, the Missouri native was enshrined into the Pro Football Hall of Fame as a result of his outstanding performance on the gridiron with the New York Giants and Green Bay Packers.

Source:
Baseball Reference August 9
National Pastime
Retro Sheet
Hall of Fame
SABR Games Project
Replay The Game