The 4-3 Defense
By Jordan Renna

The 4-3 defense refers to the ratio of linebackers to defensive lineman
(respectively) and is the scheme currently implemented by the Atlanta
Falcons.  Over the past few seasons more and more teams are switching to the
3-4 with only three defensive linemen.  Interestingly enough, the reason for
the switch has less to do with the X’s and O’s of football per say. Rather, the
switch is due in large part to an organizational need for the club to manage
the salary cap.  By switching to four linebackers teams can save, on average,
over $205,000 (based on salaries from the 2004 NFL season) and even more
when considering signing bonuses.  Then, teams can use less experienced
(read as cheaper), more athletic linebackers (now there are 4 on the field
instead of 3) so that they can go out and get that high priced impact free
agent that all of the team’s fans demand they add.

For the teams that decide to stay with the four down-lineman, they can bring
in large, heavy run stopping gap-fillers, more quick and athletic pass rushers
or some combination of both.  Nonetheless, the team will have 2 pass rushing
defensive ends that will try to attack the quarterback.  One will line up on
the strong-side (the side of the ball where more offensive linemen line up) and
try to fill the strong-side C gap, the one between the strong- side tackle and
tight end.  The other defensive end will usually match up one on one, try to
attack the quarterback and force the play to the inside. 

Both defensive tackles look to fill the gaps on runs and then collapse the
pocket on a pass.  The nose tackle attacks the A gap between the center and
the weak-side guard and the up tackle attacks the B gap between the strong-
side guard and tackle. 

With only three linebackers, teams will only put one linebacker on the weak-
side (Will).  On a running play the Will looks to help fill the hole and to
prevent the playing form going outside.

The middle linebacker (Mike) usually lines up 5 yards deep over the center
and is responsible for stopping the run up the strong-side A and B gaps.  He
usually calls out pre- snap adjustments and always attacks the blockers.

The strong side linebacker (Sam) is responsible for picking up the tight end
on a pass play and preventing the run from bouncing to the outside.

Football is an amazingly complex game with many different schemes and
even more variations of each type of scheme.  This should provide the basics
to understanding the 4-3 defense in its simplest form.