The defensive end in football is one of the most critical positions in the defensive scheme. The successful play of a defensive end will make the job easier for several other guys on the defensive unit. In a typical scheme there are two defensive ends, one on each side of the formation. Some teams utilize a "weak" and a "strong" defensive end, that will switch sides based on the strength of the formation. The job of a defensive end actually follows the job title; hold down the end on the line of scrimmage, and don't let anything outside. While that pretty well sums it up, here are some more specific tips on how to play defensive end.
In a typical defensive front, the defensive end will line up, either on the tight end on the strong side, or the end lineman on the line of scrimmage on the weak side of the formation. Depending on what specific defense is being run, he may shade to one side or the other, or just head up.
Because he's one of the defensive linemen, the defensive end will normally start in a three point stance, with his "technique hand" down. The technique hand is the hand closest to the opponent that he lined up on. So if he's outside shade, his technique hand is his inside hand. His hips need to be higher than his eyes, and his eyes need to be looking up through the top of the facemask at the guy he's lined up on.
At the Snap
When the ball is snapped, the defensive end has to get off the ball quickly and attack the outside shoulder of his opponent. As he does this, he'll get a feel for whether the lineman is coming out to block hard, or settling in for a pass block.
If his butt starts to sink and he's settling in with his hands inside, it's a pass play. In this case, the defensive end will turn his hips towards the target (the quarterback) and use whatever moves he has in the arsenal to get a sack, or disrupt the throw.
If the lineman drives out and tries to move him, it's most likely a run play. In this case, the defensive end will fight pressure with pressure. If the offensive lineman is trying to get to the outside shoulder of the defensive end, he needs to fight that pressure and stay outside. The defensive end is on his way to a successful play if he keeps his outside arm and leg free at all times, and squeezes down the gap he's playing.
What Makes a Great Defensive End?
A great defensive end has strong legs, and quick feet. He's generally taller, allowing him to get to the quarterback or at least disrupt the throwing lane. He has to be able to get separation from whichever blocker (or blockers) are trying to manhandle him. He's able to quickly read (sometimes before the snap) whether it's a pass or run play, and adjust his rush accordingly. Nothing gets outside him, and if they try to run inside him, the gap is usually occupied with the rear end of the lineman he's working on.