Drafted in the sixth round of the 1995 NFL Draft by the New York Giants, Duff played in all but one of New York's 16 regular season games, starting two at defensive end, and recording four sacks. After spending the 1996 season on injured reserve with a foot injury, Duff signed with the Washington Redskins, playing 26 games over two seasons (1997-98) and recording five sacks. After Duff was released, he appeared in training camp with the 2000 Oakland Raiders, but did not make the team.