Why is it called a nickelback in football?

Why is it called a nickelback in football? A nickel is the name for coins in the United States that are worth 5 cents, hence the term nickelback. Today, with teams at the college and professional level opting to throw more and spread the field, many defenses have countered by playing a nickelback on almost all downs.

A nickel is the name for coins in the United States that are worth 5 cents, hence the term nickelback. Today, with teams at the college and professional level opting to throw more and spread the field, many defenses have countered by playing a nickelback on almost all downs.
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