A "nickel" defense with three cornerbacks, lined up against an offense playing three wide receivers
In American football, a nickelback is a cornerback or safety who serves as the fifth (in addition to the typical four) defensive back on the defense. A base defense contains four defensive backs, consisting of two cornerbacks, and two safeties. Adding an extra back makes five, hence the term "nickel", which is the name for 5-cent coins in the United States and Canada. Usually the nickelback will take the place of a linebacker, so if the team were to be in a 4–3 formation, there would now be four linemen, only two linebackers and five defensive backs creating a 4-2-5 formation. However, some teams will replace a lineman rather than a linebacker, creating a three linemen, three linebacker and five defensive back alignment, a 3–3–5 formation. If an offensive team always uses three or more wide receivers, a defense may turn to a nickel defense for their base package on most plays. Usually extra defensive backs, such as a nickelback, are substituted into the defense in situations where the opposing offense is likely to attempt a forward pass, such as 3rd-and-long, or when extra receivers are substituted into the opposing offense.
The nickelback is the third cornerback or safety on the depth chart. The nickelback is not considered a starting position because the starting formation for a defense has only two cornerbacks and two safeties. Defensive formations with three or more cornerbacks (or three safeties) are used often enough that a nickelback will usually see moderate playing time (particularly in the modern, pass-oriented NFL) as well as subbing in for the starting corners. In certain packages (or if injuries depleted the depth chart), smaller free safeties or strong safeties can fill the spot of nickelback, as well. Their role may become that of a pass rusher from outside the box.