The nickel is a defensive formation feature five defensive backs.
Standard defensive formations have four defensive backs: two safeties and two cornerbacks. A nickel is a variation where a fifth defensive back is inserted into the game, usually in place of a linebacker. Originally the formation was conceived and employed to combat passing teams and formations featuring many receivers. Today it is often used against Spread offenses.
Some teams use a nickel as their base set running a 3-3-5 or 4-2-5 defense. The fifth defensive back in those teams is usually a player dedicated to that position. Other teams use an additional safety or an additional cornerback as their fifth defensive back.
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