Football glossary.

11 personnel is the modern game's default grouping — one back, one tight end, three wide receivers. Why every level runs it.

12 personnel pairs two tight ends with one back and two receivers. The heavy package that forces a base defense.

21 personnel is the I-form heritage grouping — two backs, one tight end, two receivers. Where it still wins.

The apex defender is the overhang LB or nickel a QB reads on RPOs. How offenses isolate him and how defenses fight back.

An audible is a QB-called play change at the line of scrimmage. The pre-snap adjustment that beats a defense before the ball is snapped.

BOB stands for Big-On-Big — offensive linemen on defensive linemen, back on the linebacker. The default pass protection scheme.

Box count is the number of defenders within five yards of the line of scrimmage. The pre-snap math behind every run/pass decision.

Bunch puts three receivers in a 2-3 yard cluster. The natural-rub formation that breaks man coverage.

Chip protection has the back briefly hit an edge rusher before releasing into a route. The compromise between protection and pass game.

A conflict defender is the unblocked player an RPO QB reads to decide run or pass. The whole RPO menu lives or dies on his honesty.

Dime replaces two linebackers with two extra defensive backs. The obvious-pass package that loads coverage.

Empty splits all five eligibles out, removing the back from the backfield. The pure pass look that forces a defensive declaration.

Half-slide protection has the line slide one direction while the back BOBs the backside. The hybrid scheme most pros use.

A heavy box has eight or more defenders inside the tackles. The run-stopping look that opens up shots downfield.

A light box has six or fewer defenders inside the tackles. The numbers advantage that tells offenses to run the ball.

The Mike is the middle linebacker — the defense's signal-caller and the player offenses identify on every snap.

MOFC means a single safety in the deep middle. The pre-snap key that tells QBs which routes are live.

MOFO means two safeties splitting the deep field. The pre-snap key that opens up post and seam routes.

A naked bootleg has the QB roll out opposite the run action with no protector. The misdirection shot that punishes fast-flowing defenses.

Nickel replaces a linebacker with a fifth defensive back. The base modern personnel grouping against 11 personnel.

An option route lets the receiver pick his break based on the defender's leverage. The trust-based concept that beats every coverage.

Pistol shortens the shotgun depth and puts the back directly behind the QB. The hybrid that keeps run game downhill.

Play-action is a fake handoff designed to pull linebackers and safeties downhill. The most efficient throw in football.

A robber is a defender lurking in the underneath middle, looking to undercut crossers and option routes. The cover-1 standard.

Shotgun puts the QB 5-7 yards behind center for time, vision, and easier reads. The default modern QB alignment.

Single-high coverage puts one safety in the deep middle. The shell behind cover-1, cover-3, and most blitz looks.

Slide protection moves the entire offensive line one direction at the snap. The zone-style answer to twists and stunts.

A swing route has the back release out of the backfield toward the flat. The simplest checkdown and built-in screen alternative.

Trips stacks three receivers to one side of the formation. The leverage tool that breaks every defensive coverage rule.

Two-high puts both safeties on the deep field, splitting it in halves or quarters. The shell behind quarters, palms, and cover-2.