You dont have to wait for the snap but isn't it while the ball is in play not a live ball being played?
Isn't dead ball between the end of play to the ready for play whistle? The play can be started at any time once it is in play from the ready to play whistle?
Live ball is when the play actually happens from the snap?
ARTICLE 4. A dead ball is ready for play when:
a. With the 40-second play clock running, an official places the ball at an inbounds mark or between the inbounds marks and steps away to his position.
b. With the play clock set at 25 seconds, the referee sounds his whistle and either signals to start the game clock [S2] or signals that the ball is ready for play [S1]. (A.R. 4-1-4-I and II)
Don't we wait until the snap is imminent? So the play clock is well down and the centre has his hand on the ball therefore the snap is imminent and a flag can be thrown.
Game Administration Interference
ARTICLE 6. While the ball is in play, coaches, substitutes and authorized attendants in the team area may not be between the sideline and coachingline or on the field of play.
PENALTY—Administer as a dead-ball foul. First and second infractions: Delay of game for sideline interference, five yards from the succeeding spot [S21 and S29].
Third and subsequent infractions: Unsportsmanlike conduct for sideline interference, 15 yards from the succeeding spot [S27 and S29].
The ref should have penalised 5 yards, 5 yards then 15.