After the ready-for-play, each player of A who participated in the previous down and each substitute for A must have been, momentarily, between the 9-yard marks, before the snap.
Tag: 9-yard mark
Rule 1, Section 6, Article 1
Electronic communication devices including but not limited to audio recorder, Local Area Network (LAN) phones and/or headsets, mobile phones, still photograph(s), film, analog or digital video(s) and/or Internet depictions, shall not be used to communicate with a player except during an outside 9-yard mark conference (7-yard marks in nine-, eight- and six-player competition).
NOTE: Each state association may authorize the use of a drum by a team composed of deaf or partially deaf players, in order to establish a rhythmic cadence following the ready-for-play.