What do the yellow lines and shaded areas in the formation diagram mean?
The T-shaped zone (Seven yards from the snapper along the line, plus the tackle box) marks the region where offensive linemen must be positioned if they want to crackback below the waist legally. See rule 9-1-2-e. The dashed line marks seven yards behind the ball. If no player is positioned to receive the snap fewer than seven yards back, it’s a scrimmage kick formation. The shaded regions represent the narrow area between linemen (whose heads must break the plane of the snapper’s waist) and backs (who must be entirely behind the snapper’s body other than his legs and feet). A player in that narrow region is neither a lineman nor a back, and unless he’s a hand-to-hand quarterback, the formation is illegal.
