Goal: disrupt the running game and sack the quarterback
The difference between a 4-3 defensive lineman and a 3-4 defensive lineman is not only in the physical characteristics, but also in the philosophy of the defensive schemes themselves. In a 3-4 defensive structure the primary objective of the three defensive lineman is to occupy the blocks of two offensive lineman as long as possible. This keeps the linebackers unblocked and free to run and pursue the ball. In order to accomplish that role, they must be very big.
The 4-3 defensive lineman on the other hand are not as big. Most 4-3 games count on their defensive lineman to penetrate and disrupt the offensive line of scrimmage. These linemen, based on that philosophy, are not as big but are extremely quick and explosive.
In a four man front there are two defensive tackles who align on the guard or center. If you want space eaters they play the defensive tackle position in a 4-3.
In this pass-oriented game today as well as the fast-paced no huddle offense that has filtered into the NFL, these space eaters have become less common. The defensive tackles have gone from primarily a run stopping position to a smaller, quicker, better conditioned inside rusher. Rushing the passer is more taxing on the defensive tackles than the run game. Defenses are rotating at least three defensive tackles during the game to help keep players fresh. Tired lineman can’t rush effectively.
The other two defensive lineman in the 4-3 scheme are the defensive ends. These players align on the offensive tackle or tight ends. They are taller, faster and they are the best pass rushers in a 4-3 scheme.
Their primary role is to disrupt the outside running game and most importantly sack the quarterback. Different than the defensive end in the 3-4 who eats up blocks for the linebackers and allows them to pursue and tackle, the 4-3 defensive end is a play maker himself. They are expected to produce with tackles, pressures, sacks, and quarterback hits. The 4-3 defensive end should be the most impactful position in the scheme to be an effective defense.