In American football, a spy is a defensive player assigned to cover an offensive backfield player man-to-man when they are expected to engage in a running play, but the offensive player does not run with the ball immediately.

This strategy is generally used with "dual-threat" quarterbacks who may be expected to run on their own after expected passing plays break down, with the defensive player floating near the line of scrimmage, following the quarterback's movements.[1]

Spies are also sometimes known as "keys".[2] Generally, spies are linebackers.[3]


  1. ^ "Spying the Quarterback". Sporting Charts. Retrieved 17 January 2017.
  2. ^ "Football Outsiders Glossary: General Football Terms". Football Outsiders. Retrieved 17 January 2017.
  3. ^ Theismann, Joe (2003). The Complete Idiot's Guide to Football. Penguin. p. 179. ISBN 0786548363.