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Football Defensive Schemes In order for coaches and players of American football to exchange information in a rapid manner during practices and games, a more or less standard terminology for defensive schemes has been developed.
Basic alignments Players on the defensive side of the ball are generally split between down linemen (tackles, defensive ends and nose guards), linebackers, and defensive backs (safeties and cornerbacks). To describe the basic defensive alignment of linemen, linebackers and backs, the number of down linemen is usually followed by the number of linebackers. By far the most common alignments are four down linemen and three linebackers (4-3), but alignments with three down linemen and four linebackers (3-4) are currently used by a number of teams. The number of defensive backs is usually not mentioned. However, on plays where the defense expects the offense to pass, emphasis is often placed on the number of defensive backs. When one of the "front seven" (down linemen and linebackers) is removed in favour of a defensive back, the five defensive backs are described as a "nickel" package. When a sixth defensive back is inserted, it is known as a "dime" package. Unusual defensive alignments are rare, but often successful. In Super Bowl XXV, the New York Giants played with only two down linemen, with four linebackers and five defensive backs. The strategy was very successful in preventing the Buffalo Bills from completing long passes, but it allowed over 190 yards in rushing. Nevertheless, the Giants won. Another example is the New England Patriots using no down lineman and seven linebackers for two plays against the Miami Dolphins during a Monday Night game in 2004. Even in obvious running situations, the defense must be able to account for the eligible receivers on offense. There are two general schemes for defending against the pass: Man-to-man, where each eligible receiver is covered by a defensive back or a linebacker. Zone, where certain players (usually defensive backs or linebackers, though occasionally linemen are too) are assigned an area on the field that they are to cover. In most cases, man-to-man coverage is more effective against short passes, while zone coverage is effective against long passes. To create a shorthand, most defensive schemes use the term "cover" (for pass coverage) and a number to describe a combination of schemes. As in American Football there are only five eligible pass receivers on a given play (technically the quarterback is also an eligible receiver, but passes to the quarterback, though known, are rare) while there are at least seven pass defenders in 3-4 alignment in man-to-man defense, some of the pass coverage personnel may either blitz (cross the line of scrimmage with the down linemen in an attempt to sack the quarterback), provide double coverage on a receiver, or help other defensive players with the pass coverage. In zone coverage, all defensive linebackers and backs have a pass coverage assignment.
Generally speaking, the effectiveness of a defense against short passes and the run drops as it goes from Cover Zero to Cover Four, but their effectiveness against deep passes increases. Bracket: A Double team scheme to take away a certain receiver. There are two types of Bracket coverage: High/Low & In/Out. High/Low coverage involves one defensive player staying between the line of scrimmage and the receiver, protecting against short routes, and another player behind the receiver to protect from deep routes. There are numerous ways to beat this coverage with skilled personnel, however, based on running a route that breaks to the inside. On an "in" route the receiver would make a ~90 degree turn to the inside of the field and use his speed to separate from the underneath defensive back. A higher difficulty option is the "post, or "skinny post", route, which involves a turn of ~30-60 degrees to the inside. The receiver again uses his speed to separate from the underneath defender, and the quarterback must deliver the ball over the underneath defender and far enough inside that the defender protecting against deep passes can not come down/across the flight path of the ball and deflect or intercept it. Though the difficulty on this pass is much higher, it can be used to gain many more yards. In/Out coverage works just as it sounds, with one defender protecting against routes run to the inside and another protecting against routes to the outside. The easiest way to beat this coverage is a simple go/streak route: the receiver simply sprints down the field past the defenders. Any hesitation on the defenders' part to drop their coverage assignment and run with the streaking receiver can be exploited. Zone Blitz: A defensive stunt where a LB or DB Blitzes and a Defensive Linemen replaces the LB or DB in Coverage. The creation and refinement of this scheme is most often credited to Dick LeBeau, defensive coordinator for the Pittsburgh Steelers. Effective defense depends on co-operation from defensive players and an understanding of what coverage they are in. For example, in Cover Two, the cornerbacks are afforded with the knowledge that if they decide to jump a route (and thereby intercept or deflect a pass) they will have safety help farther upfield should they be tricked by a fake. In Cover One, the safety must be aware that one of the cornerbacks could have difficulty covering a wide receiver, and must be available to move over to help the cornerback before the quarterback can throw. Typically Cover One is only used if there are more than two wide receivers or other passing threats. Moreover, mixing up defensive alignments and not being predictable are important since if an offense recognizes an alignment or coverage scheme, or a tendency to use such a scheme, they can often take advantage of it. For example, if the defense is blitzing, and the quarterback forsees it (for example, one of the blitzing players moves towards the line of scrimmage before the snap) the quarterback knows that it is man-to-man coverage and will look for his fastest receiver to get open, or throw to the spot that is vacated by the blitzing player. In the modern game, with players getting faster and stronger, defensive coordinators often look to a player's special skills in order to surprise the offense. For example, in some defensive schemes, defensive down linemen are given pass coverage responsibility. Since Lawrence Taylor demonstrated the effect of a single blitzing linebacker on an offensive line's blocking scheme, most teams now rush three down linemen and a single linebacker (often a different one on every play), a strategy that was almost unknown before he started to play. Moreover, even defensive backs are being given more responsibility on running plays. For example, on plays where a running back runs wide, it is the responsibility of the cornerback to ensure that the running back does not get directly to the sideline, and that the back is forced to run in front of the cornerback where there is more likely to be help from linebackers. Modern offenses have adapted to these strategies, and often require different skills from players, particularly running backs who, in addition to running with the ball, are expected to run deep pass routes against linebacker coverage, and to be available to block blitzing players on pass plays.
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