The base defense in football is the defense most often used by the defensive team. Basically, it serves as a �default� defense, and other variations and schemes can be added to create pressure and confuse the offense.
3-5-3 Defense – In the last decade, this type of defense has been used extensively on the college and high school level. It utilizes three defensive linemen, five linebackers and three defensive backs.
3-4 Defense – While it suffered through a decline, the 3-4 defense has increased in popularity in recent years. Used throughout all levels of football, it employs three linemen, four linebackers and four defensive backs.
Today, teams which use the 3-4 as their base defense include the Dallas Cowboys, Pittsburgh Steelers, San Diego Chargers, New England Patriots and New York Jets. The 1972 Miami Dolphins were the first team to win a Super Bowl using the 3-4 defense.
4-3 Defense – The most frequently used defense in the NFL, the 4-3 uses four defensive linemen, three linebackers and four defensive backs. The formation was created by Tom Landry in the 1950s while he was the Defensive Coordinator of the New York Giants.
Originally intended to stop Browns running back Jim Brown, the 4-3 is popular for its ability to protect against both the run and the pass. Many variations of the 4-3 also exist, as each team adds their own unique twist.
4-4 Defense – An attacking defense, the 4-4 often uses numerous blitz packages to pressure the quarterback and force turnovers. The greatest drawback is that there are only three men in the defensive backfield, and that sometimes leads to big plays from the offense.
Many other base defensive alignments are available, including the 5-2, 3-3-5 and 5-2-4. While some of these might be used on a situational basis in the NFL, the most common base defenses in the pros are the 3-4 and 4-3.