Nickel defense

In American football, a nickel defense (also known as a 4–2–5 or 3–3–5) is a defensive alignment that uses five defensive backs, of whom the fifth is known as a nickelback. Although the modern definition of the term encompasses all formations featuring five defensive backs, the original and still most common form of the nickel defense features four down linemen and two linebackers. Because the traditional 4–2 form preserves the defense's ability to stop an opponent's running game, it has remained more popular than its variants, to the extent that even when another formation technically falls within the "nickel" definition, coaches and analysts will refer to it by a more specific designation (e.g., "3–3–5" for a lineup of three down linemen and three linebackers) that conveys more information with equal or greater conciseness.