Answer:
Cal Hubbard (Robert Calvin Hubbard) was the only man elected to both the professional baseball and football halls of fame as of 2012.
He played tackle for Green Bay, Pittsburgh and the New York Giants and was elected to the National Football League's Hall of Fame in 1963. He was also inducted into the College Football Hall of Fame in 1962.
He was elected to the Baseball Hall of Fame in 1976 as only the fifth umpire to be honoured.
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