In general there are three different types of defensive players: linemen, linebackers and backs.

Defensive Linemen are big, strong and quick capable of stopping the run and pressuring the quarterback. Typical D-linemen are called Tackles, Nose Guard or Ends.

Linebacker is the single most athletically versatile position in football. Linebackers must read the offense and respond instantly to what it is doing. On any given play and defensive scheme, a linebackers may be asked to stop the run or on passing plays cover a receiver [typically a tight end] or blitz the quarterback. There are different types of linebackers but the distinction is a funtion of the defensive scheme that the team has adopted.

Defensive Backs are primarily responsible for pass defense and run support. They must be fast, tough and smart to execute the complex defenses that are run by college and pro level teams. The two types of D-backs are corner backs and safeties.

The Blitz- If the offense is protecting their quarterback too well, a defensive coach might need to throw a surprise. Typically this surprise might be to blitz one or more linebackers or defensive backs. This often causes a sack, hurried throw or best yet, a badly thrown ball and a turnover.

The blitz is a high risk defensive tactic. By blitzing linebackers and d-backs, one or more of the receivers are not covered. If the play is a run, its a toss up as to whether the running back will run right by the blitzing linebacker or meet him in the hole. If the QB can pass the ball to his receiver before the blitz gets to him, the QB is said to have burned the blitz.

The 3-4 Defense This is a defense common in the NFL. It always has three down linemen and four linebackers. The 3-4 defense is a challenging defense to run. If your linemen aren't up to it, the overall defense will give up too many rushing yards. It also requires having a number of linebackers that can perform at a high level.

D-linemen in the 3-4 are called either Tackles or Ends and the man in the middle is called the Nose Guard or Nose Tackle (NG or NT). An NFL nose guard is a real monster who expects to be double and triple blocked and still gets sacks.

In the 3-4 defense, the two inside line backers are called Interior Linebackers or ILB. The linebackers on the outside are called Outside Linebackers (OLB) and are expected to handle run plays that go outside. Sometimes 3-4 linebackers may be asked to drop into pass coverage.

D-backs in the 3-4 are fairly standard pair of corner backs and safeties. The Strong Safety (SS) will always line up on the tight ends side of the formation. The Weak Safety will line up on the side without a tight end.

The strengths of this defense are that it is typically fast, athletic (with so many linebackers) and handles the pass very well.

The downside is that it can usually be had by the run- particularly disguised runs like a draw or a delay. Injuries to linebackers and depth become a key issue over the course of the season.

The 4-3 Defense

By far the most common defense at the college level is the venerable 4-3 which consists of 4 D-linemen, 3 linebackers.

Defensive Linemen in the 4-3 scheme are called Tackles (RT or LT) or Defensive Ends (DE).

Linebackers in the 3-4 scheme are called the Strong Side Linebacker or SAM (TE side of the formation), Middle Linebacker (MIKE) and Weak-Side Linebacker (WILLY). The actions of the three linebackers in this set are designed to compliment and support each other.

The four defensive backs in the 3-4 set are two corner backs and a Strong and Weak safety.

The strength of the 4-3 defense is its balance. The 4-3 works well against the run and the extra lineman provides more consistent pressure on the QB on pass plays.

The weakness of the 4-3 defense is speed in the middle. Without a fourth linebacker, short, quick passes will riddle the short zones and loosen up the linebackers. The 4-3 can be fooled by play-action passes where the QB fakes a handoff or a pitch mimicking the look of a running play and then throws the ball down field. If the linebackers and/or the defensive backs are fooled, they can be burned badly by the play action pass.

The 5-2 Defense

A common defense used in obvious short yardage situations in college and pro ball is the 5-2. It has five down linemen and two linebackers.

Defensive linemen in the 5-2 set are called Nose Guard or Tackle (NT), Right and Left Tackles (RT, LT) and defensive ends on either side.

The two linebackers in the 5-2 are the Strong and Weak side linebackers which position themselves relative to the side the offensive Tight End lines up on.

The defensive backs are a pair of corner backs and a pair of safeties.

The strength of this defense is that it is very difficult to run against five down linemen.

The weakness of this defense is the pass in general.