|This article does not cite any references or sources. (July 2009)|
The 4–4 defense is based on speed, athleticism and intelligence rather than on size and strength. Versatility is key because every player may have to change roles from one play to the next. It is an attacking defense stocked with multiple blitz packages that can easily be concealed and altered. The top priority of the 4–4 defense is stopping the run by keeping eight men close to the line of scrimmage. This also makes it difficult for the offense to identify where the pressure comes from when the defense blitzes. One other significant advantage of the 4–4 defense is its flexibility and adaptability. The 4–4 can shift into nickel or dime coverage quickly and easily.
On the other hand, the 4–4 defense is vulnerable to the big play, both through the air and on the ground. Running backs with breakaway speed can be very successful against the 4–4. Once the running back clears the front eight, they may only have one or two men to beat in the secondary.
Another way this defense can be exposed is with the deep pass. The cornerbacks are often left exposed without safety help, either in man coverage or a 3 deep zone. If a Wide receiver manages to clear his defender, there may be nothing between him and the End zone. However, even if a Wide receiver does open up deep, the 4-4 defense can bring considerable pressure on the opposing Quarterback to stop him delivering the ball.
While size is definitely a plus for defensive tackles in the 4–4, its not as important as quickness and the ability to use leverage to manipulate the offensive linemen. It's imperative for the defensive tackles to hold their ground. They cannot allow themselves to get turned around and under no circumstances can they allow themselves to be base blocked, one on one. Again, size is great and certainly helps, but a smaller tackle can be just as effective if he is a good technician. In the base 4–4, the defensive tackles will generally line up in the B gap in a 3 technique (outside eye of the guard). Depending on the read, the defensive tackle will either be asked to penetrate the line of scrimmage, or hold his ground and attempt to take on both the guard and offensive tackle.
The defensive end's primary role in the 4–4 defense is to get to the quarterback as fast as possible. They need to be strong enough to fight their way past offensive tackles; but they also need to be athletic enough to act as linebackers because there are plenty of scenarios in the 4–4 defense that require the defensive ends to drop into coverage, just as an outside linebacker would do. The ends should do whatever they can to get to the quarterback and on running plays they should pursue down the line of scrimmage, but be careful not to over-commit as they need to be ready for a potential cutback.
There are two inside linebackers in the 4–4 scheme sometimes known as the Mike and Buck linebackers. While they both play inside, Buck will shade to the strong side of the offense, Mike shades to the weak side. It is important for these inside backers to be aggressive and have a nose for the ball. As in most defenses, the Mike backer acts as the quarterback of the defense and is often the defensive leader. The primary responsibility of both Mike and Buck is to stop the run. The Buck backer will generally be more active in pass coverage than the Mike. Because of this, the Buck backer needs to be athletic enough to drop and almost play like a strong safety.
As there are two inside linebackers, there are also two outside linebackers. These outside backers are known as Sam and Rover. The Sam linebacker typically sticks to the strong side. Sam does his fair share of blitzing, however he also needs to play the run and will usually be relied upon to cover the tight end or potentially a back out of the backfield. Rover will generally play on the weak side, however he can be moved to just about anywhere to better suit the defensive call or adjustment. The rover is probably the single most versatile position in the 4–4 defense. Depending on the call and the personnel in place, the Rover’s job could be purely to get after the quarterback or to drop into coverage. In a blitzing situation, the Rover is the most likely player to get to the quarterback. The Rover position can be played by a variety of athletic types ranging from an outside linebacker, to a strong safety. The "Rover" linebacker is sometimes also known as the "Will" position (Sam comes from strong side linebacker, and thus Will signifies the weak side backer).
The cornerbacks are often on islands in man coverage or in a deep zone, and they need to possess exceptional speed and change of direction skills. They also need to be intelligent when diagnosing the play and when in zone coverage, must be able to play the ball. The corners will generally line up 3 to 5 yards off the ball, but will rarely jam because of the risk of a big play. If the corner jams and the receiver is able to get past him, it has a high probability of ending up a big play for the offense. Of course it helps to have corners that can assist in run support, however, their primary responsibility is to shut down any receiving threat they are assigned to. The safety in the 4–4 defense should be one of the team’s better athletes. He needs to be fast enough to play in coverage and strong enough to help against the run. He needs to have a nose for the ball and be able to diagnose the play to put himself in a position to make a play. The safety will almost always be assigned to the deep middle of the field, however he can also be blitzed in various packages.