Here you can compare and contrast the two basic sets — the 4-3 and the 3-4 — defenses in the NFL utilize on most plays.

Here's a quick overview of their two options:

• The 3-4 defense uses three down linemen and four linebackers.
• The 4-3 defense uses four down linemen and three linebackers.
• The 3-4 defense is quicker because of the extra linebacker.
• The 4-3 defense tries to occupy the offensive linemen with the four defensive linemen, keeping the linebackers free to run and make plays.
• Most NFL teams use the 4-3 defense. 

The 4-3 defense is a gap-control defense designed to keep the offensive linemen off the three linebackers. By lining up in the gaps, the defensive linemen are better able to control the offensive line. This frees up the linebackers to run to the football.

The 3-4 defense is quicker because it has four linebackers. This defense relies on a dominant nose tackle that can command a double team on each play. An effective nose tackle clogs the middle, enabling the linebackers to run and make plays on the ball.