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In American football, the 3–3–5 defense is a defensive alignment consisting of three down linemen, three linebackers, and five defensive backs. The 3–3–5 defense can also be referred to as the 3-3 stack and the Spread Defense. It is one form of the nickel defense, a generic term for a formation with five defensive backs. Veteran college football defensive coordinator Joe Lee Dunn is widely credited with being the main innovator of the 3-3-5 scheme.
This alignment is generally used when the defense is trying to confuse the offense by applying different blitz pressures on the offense while playing mostly zone or sometimes man coverage. This alignment is rarely seen in the NFL[why?], but is used by many high schools to counterattack the spread offense scheme. Boise State, West Virginia, BYU, and Arizona have used this formation with success in college football. Michigan ran this formation during the 2010 season. TCU uses this as a variant formation; its base defense is a different nickel set, the 4–2–5.
Teams that run the 3-3-5 generally use it because they are a relatively fast but smaller unit compared to the opposing offense, and they want to cause blocking assignment issues for that offense. Also, a 3-3-5 can be adjusted to a 4-3, 3-4, or 4-4 defense with the same starting players.
To effectively play the 3-3-5, the "Front 8" (e.g. the eight defensive players closest to the line of scrimmage) must be physical and tough. The three down lineman must be able to control the running lanes, execute an effective pass rush, and be able to keep the opposing offensive line occupied so that the linebackers can make plays. The two outside or "Stud" linebackers must be effective at pressuring the offensive line and reading and reacting to the play as it develops. The middle linebacker (also known as the "Mike" linebacker) must be able to effectively move in the direction the play is going (also known as "flowing to the ball") while also being able to shed blockers and make plays.
The defensive secondary must be equally capable of pressuring the offensive lineman and dropping back into pass coverage. In particular, the strong safety is the most versatile athlete on the field as on any given play he can drop in coverage, pressure the quarterback, or play a "Mike" linebacker if the defense switches to a 3-4 alignment. In this alignment the free safety is generally the best playmaker and smartest athlete on the defense.