What it is

The offense lines up in a way the rules do not allow. At least seven players must be on the line of scrimmage, and the players at both ends of that line must be eligible receivers.

The penalty

The penalty is 5 yards, and the down is replayed. The officials flag it before or at the snap and the penalty is enforced from the line of scrimmage.

More detail

Offenses sometimes use unusual formations on purpose, so they tell the referee which players are eligible receivers to keep them legal.

Animated play

Blue circles are the team with the ball. X marks the other team. The yellow oval is the ball.

1. The rules say at least seven offensive players must be on the line of scrimmage at the snap.
2. Here only five are on the line, and the others are standing a step behind it.
3. The official throws a flag before the play starts. It is a five-yard penalty and the down is replayed.