A counter in football is a kind of run play used to fool the defense. It employs running backs, blockers, and the quarterback. Numerous iterations of the counter have been developed to mislead defenses.
The purpose of a counter is to make the defense think the ball is going in one direction when it is actually going somewhere else. To do this, the offensive line will, for instance, block as if the ball carrier is going to run to the right. Instead, he runs to the left in an attempt to catch the defense off guard. A counter may involve the quarterback faking a handoff to one running back, before giving it to another. The play may even call for the quarterback to take the ball himself.
The counter trey is a popular example of counter used by many teams. In it, the running back starts to run to one side before cutting back the other way with the help of down blocks, which are blocks made by offensive linemen toward the center position on the line of scrimmage. Pulling offensive linemen, a term for blockers who relocate from the backside of the field, away from where the play is happening, help block for the running back.