The defensive backs (also called secondary ) are the last line of defense (after the defensive linemen and line backers ) of the Defense in American Football.
The defensive backfield consists of safeties and cornerbacks, whose main task is to defend the opponent's passing game. In the typical defensive formations 3-4 Defense ( three defensive lineman and four linebackers ) and 4-3 Defense ( four defensive linemen and three linebackers ) there are two safeties and two cornerbacks. The safeties are a Strong Safety is also used near the line of scrimmage in defending the run game and the Free Safety who is responsible as the last man in particular for the defense deeper passes. The two cornerbacks to play as a man-marker close to the opponent's wide receivers in order to deny them pass catches. This is pure man coverage ( one to one coverage ), in which the cornerbacks with their respective receivers even switch the attack side, up to the zone defense ( zone coverage ), in which the cornerbacks receiver in their zone with the safeties and some and line backers, flowing to take and pass.
Bring the Defense more than four defensive backs on the field ( in obvious pass situations or because the opposing offense three or more wide receiver sets up ), the Defense brings a fifth defensive back, the so-called Nickelback, for a defensive lineman or a linebacker. The Nickelback is another cornerback, whose name comes from the U.S. 5-cent coin ( nickel) is derived. Bring the Defense an additional, sixth, defensive back for a defensive lineman or line baking, so this is also usually a cornerback and dime back is called. The term dime is derived from the American 10-cent coin ( dime ), as two nickel give a dime.
More rarely, there are also the so-called Quarter -Defense (based on the next larger coin: the Quarter - dollars), in which a seventh defensive back coming into the field. This is often a safety because the third safety of a team is usually better than the fifth cornerback. This also Prevent Defense ( dt ) prevent -called defense is almost exclusively used when the opposing offense is still trying to score a touchdown with a Hail Mary pass just before the end. As the name suggests, is only trying to prevent the dot gain, while a short -or medium- space gain is accepted in case of doubt. To avoid confusion with the captain of the offense, the quarterback, the seventh defensive back is called but not quarterback.
- Football position