A term in football that describes a short pass from the quarterback to a receiver when all other passing options are covered downfield. A tailback typically serves as the receiver in this situation.
Any designed pass play will typically have more than one option for the quarterback to choose from, but if the defensive coverage is too well-played the quarterback needs an alternative target. The "safety valve" usually comes in the form of a running back who has advanced past the defensive line (most often after remaining to block)-as the pass rush closes in or the quarterback is flushed out of the pocket, a short pass option is still available to prevent a wasted play or loss of yards.
The term "safety valve" is also sometimes used to refer to the defensive position of safety.