Complex sentence: Gillman was inducted as a coach into the Pro Football Hall of Fame in 1983 and the College Football Hall of Fame in 1989--the sole coach in the history of American football to have earned both honors.
Split into simpler sentences: Gillman was inducted as a coach into the Pro Football Hall of Fame in 1983 and the College Football Hall of Fame in 1989. He is the sole coach in the history of American football to have earned both honors.