also: force · contain · the force defender
The defender responsible for turning a run back inside. Everything outside him is his fault, and the offense has a block assigned to him.
The defender who owns the outside edge of a run: his job is to keep the ball from getting around him, so the runner is turned back into pursuit. Which player it is changes by front and by call, and can be a defensive end, an outside linebacker, a corner or a safety on the same defense in different weeks. Coaches name the two secondary versions: Cloud is corner force, and Sky is safety force. With a corner forcing, the safety fills the alley, the space between the core of the formation and the corner.
force, contain playerspill player, overhang, the alley playerThe paired idea is spill, and neither word means much alone. Where a force player turns the ball outside-in, a spill player attacks a block from the inside out to push the ball wider, into the force. A defense decides which of its players does which. Spill is its own term rather than another meaning of force.