A defensive lineman is any of the down positions on the defensive side of American football. Although alignments vary, the most popular consist of either 3 or 4 down linemen. On a 3 lineman set, there are 2 Defensive Ends which bookend an often large Nose Tackle. In a 4 lineman set, the Ends bookend 2 Defensive Tackles. The primary job of a defensive lineman is to gain penetration past the line of scrimmage to disrupt an offensive play. The best results are a sack on the quarterback or tackling a ball carrier for a loss of yardage.

Bruce Smith is the NFL's all time sack leader; he currently plays Defensive End for the Washington Redskins. Other notable defensive linemen throughout NFL history include Reggie White (DE), Elvin Bethea (DE), Art Donovan (DT), Joe Greene (DT), David "Deacon" Jones (DE), Bob Lilly (DT), Howie Long (DE), Gino Marchetti (DE), Merlin Olsen (DT), Alan Page (DT) & Randy White (DT).