Duncan has a good frame for an offensive tackle, standing at 6'6" and weighing around 310 pounds. He has long arms and a solid build. Duncan has a thick lower body and carries his weight well, which helps him anchor against powerful defenders. Duncan is a surprisingly athletic tackle for his size, with good quickness and agility. He has a quick first step and can effectively reach the second level. He also moves well laterally and has good footwork in pass protection. He could benefit from improving his overall speed and explosiveness. He has a strong initial punch and can reset his hands effectively to maintain his blocks. Duncan also has good leverage and anchor strength in the running game, which helps him create movement at the line of scrimmage.