Defense in the foundation of any good football team. Football coaches are fond of saying that offense wins games, but defense wins titles. This concept goes all the way back to youth football leagues, where a dominant defense is the #1 key to a successful season. The reason for this is simple; if the opponent never scores, a team can never lose.
Defense is pitted against the offense, trying to defend one’s end zone from a score. If defenders make big hits on an opponent, they can rattle the other team and wear them down physically.
Defense tends to highlight brute force. Linebackers and safeties come up to punish a running back, who might run the ball twenty or thirty times a game. Defensive ends and blitzing players try to hit the quarterback, either rushing his throws or hurting him too much to be an effective passer.
A defensive tackle is an interior lineman on a defense. These players are the biggest defenders on the field, and their job is to stop the opponent’s running game.
These players stop the run, but are also highly skilled pass rushers. Especially in the 4-3 defense, these players tend to combine the size to take on offensive linemen on running plays with the quickness to get around them on passing plays. In the 4-3 defense, defensive ends tend to be the sack leaders.
Linebackers are tweeners on defense. Their primary job is stopping the run, though they also must be quick enough to cover running backs and tight ends in the passing game. These players tend to be the tackle leaders. In the 3-4 defense, the outside linebackers are also sack leaders.
Are the smallest and quickest players on the defense. It is their duty to cover the offense’s wide receivers and flankers. Especially on teams which blitz a great deal, these men are left in one-on-one coverage, and therefore their mistakes are magnified as big plays.
Safeties are between linebackers and cornerbacks in size. They must be able to help cornerbacks in coverage, as well as cover tight ends man-on-man. The strong safety is often moved to the line of scrimmage to help out in run defense. This is called "eight men in the box", with the strong safety being the eighth man (the linemen and linebackers being the other seven). These players tend to be among the hardest hitters in football. The free safety stays back in coverage, helping out on double teams and roving the backfield looking for interceptions.
The standard rush package is four players, usually the "down linemen", or those that put their hand down in a stance. When more than four defenders are used to rush the passer, this is called a blitz defense. This is meant to overwhelm the offensive line with too many people to block.
The zone blitz is meant to fool an offensive team. This means that players who normally rush the passer are dropped off into a zone pass coverage, while players not usually accounted for in pass blocking schemes are sent after the quarterback.
Often, the zone blitz attempts to overload one side of the line with blitzers, making it impossible for offensive linemen to block every defender. Though this can be effective when employed, the zone blitz leaves gaping holes in run defense and mismatches (lineman versus receivers) in pass defense.
A nickel defense is a personnel alignment specifically designed to stop the pass. This means that a linebacker is taken out and replaced by a defensive back, whose specialty is pass coverage. Since there are normally four defensive backs on defense, the insertion of a fifth defensive back is naturally called a "nickel" package.
An insertion of a sixth defensive back is called a "dime" package. More so than the nickel defense, this is built for pass coverage. The insertion of the seventh defensive back is called a "quarter" package, though it is more commonly referred to as a prevent defense. This is because such personnel alignments usually come at the end of a half, when it is known that the offense will be passing. It is called prevent, because it hopes to prevent a big play.
There are several different kinds of defenses, though two of them are more prevalent than all others. These are the 4-3 and 3-4 defenses.
The 4-3 Defense
These numbers tell you how many lineman and linebackers are on an offense. The first number describes the number of lineman, while the second number describes the number of linebackers.
The 4-3 defense has been the traditional alignment in football since the 1950′s, when one of the defensive tackles in the 5-2 defense stood up and became the middle linebacker.
Of the four linemen in the 4-3 defense, two of these linemen are defensive tackles, whose main job is to stuff the run. The other two are defensive ends, who are smaller and quicker than the tackles. Though they must also stop the run, the ends’ strength is their ability to rush the quarterback.
In the 4-3, the three linebackers have specific duties.
The middle linebacker is the largest of the three. He patrols the line of scrimmage from sideline to sideline, trying to tackle fight off guards and fullbacks and tackling the ball carrier.
The strongside linebacker lines up over the tight end. He jams the tight end in pass coverage, and tries to fight off his block in run defense. Since a team usually run toward the tight end’s side, this means the strong side linebacker must excel in run defense.
The weakside linebacker is quicker than the other two. He is the likeliest player to be called on to blitz the quarterback. In run defense, he should be able to fight off a fullback’s block and stop end-around runs by the halfback, or pursue and run down the halfback from the back side of the play.
The 3-4 Defense
In the 3-4, there is only one defensive tackle. He is called the nose guard. This player must take on the double team at the point of attack. He seldom makes tackles, but is effective if he stands his ground and is not pushed backwards by his two opponents.
There are two defensive ends in the 3-4. These players are bigger than 4-3 defensive ends. Though they are called on to rush the passer, the defensive scheme calls on them to stop the run. Like the nose tackle, the defensive ends in the 3-4 are mainly to occupy blockers, freeing up linebackers to make plays.
In the 3-4, there are two middle linebackers. These two players should be larger than average linebackers, because they will need to take on offensive guards. Their job, too, is mainly to stop the run, though they must be quick enough to avoid being a liability in pass coverage.
The outside linebackers in the 3-4 are the pass rusher. The weakside linebacker is often brought as the fourth rusher, and tends to have the quickness to give offensive tackles fits in blocking them. The strongside linebacker must be able to take on the tight end in run blocking, but is often brought on blitzes. When the weakside linebacker is dropped into coverage, the strongside linebacker becomes the primary pass rusher, often used to fool the offensive line into blocking in the wrong direction.
The 3-4 defense was designed to add more athleticism to the defense, to put three primary run stuffers on the field (instead of two) and to make pass rush schemes less predictable. Though slighty more teams employ the 4-3 due, because the personnel are easier to find, the 3-4 has been used to great effect by Bill Parcells’ New York Giants and Bill Belichick’s New England Patriots.