Defense 101

The goal of the defense is to stop the offense from advancing the ball and scoring.  There are three main groups of positions that each player assigned to.  The defensive line, whose main responsibilities are to engage the blockers so that other players can get to the ball carrier to tackle them and disrupt the passing of the ball by the quarterback.  These player start on the line of scrimmage most of time in a 3 and 4 point stance. There can be anywhere from 3 to 5 of these down linemen and there defensive assignment is based on how many of them are on the field.  For example, in a 3-4 scheme the "3" represents three down linemen and their job is engage the offensive blockers.  But in a 4-3 scheme the outside linemen, also known as defensive ends usually have the job of containment, meaning they are to make sure the ball carrier does not get outside of them.  The second group of position players are the linebackers who are the primary tacklers of the ball carriers, but they also can be responsible for covering the receivers as well.  The number of linebackers is dependent on the number of the other positions.  Some schemes call for between 2 and and 4 linebackers on the field at one time.  The examples below show each defense.

The diagram above shows a 4-3 defense (4 down linemen and 3 linebackers)

The next diagram shows a 3-4 defense (3 down linemen and 4 linebacker)

The last group of defensive players are the defensive backs.  There job is to prevent the receivers from catching the ball and to be the last line of defense for tackling the ball carrier.  There are 4 primary defensive backs for most schemes.  Two corners who cover the outside receivers, the free safety that covers the middle of the field, and the strong safety who covers the TE or backs coming out of the backfield and also provides additional run support if needed.  Where a defensive back lines up prior to the snap depends on the type of coverage being called.

Coverage Schemes

Cover 2-meaning two deep safeties each covering 1/2 of deep part of the field.  The corners play closer to the line of scrimmage and are responsible for the flats.

Cover 3- The cornerbacks along with the free safety split the deep part of the field into thirds.  The strong safety covers the short and intermediate section of the field where the TE is lined up (strong side)

Cover 0 (also known as Man-to-man)- Each defensive is assigned to a particular receiver and they move with that receiver no matter where the route takes them.  The corners have the outside receivers and the safeties have either a slot receiver, TE, or running back.