7-2-3 Diagram

7-2-3 If the ball is snapped, this would be an illegal formation foul at the snap. Of the A players who are not on their line at the snap, only one player may penetrate through the waistline of his nearest teammate who is on the line, and he must be in position to receive the snap, even though he is not required to receive it.

7-2-3 Only one player who are not on the line may penetrate the vertical plane through the waistline of his nearest teammate who is on the line. This player (A) must be in position to receive a hand-to-hand snap, but does not have to actually receive it. By rule, he is the only player allowed to be positioned in “no man’s land” at the snap. All other players not on the line must be clearly positioned as backs. The player marked (B) is in an illegal position.