The
nickelback defense is the name of
special defensive set-up in
American football
(maybe in
Canadian football too, dunno).
In addition to the usual four
defensive backs,
a fifth defensive back, called the
nickelback, is added in place of
one of the
linebackers.
The origin of the term is a play upon
the name quarterback. The nickel is
worth five cents and the nickelback is the
fifth defensive back. Clever, huh?