"An incoming legal substitute must enter the field of play directly from his team area, and a substitute, player or departing player must depart at the sideline nearest his team area and proceed to his team area. A departing player must immediately leave the field of play, including the end zones. A departing player who leaves the huddle or his position within three seconds, after a substitute becomes a player, is considered to have left immediately.
Substitutes who become players (Rule 2-27-9) must remain in the game for at least one play and replaced players must remain out of the game for at least one play, except during the interval between periods, after a score, or when a timeout is charged to a team or to the referee with the exception of a live ball out of bounds or an incomplete forward pass (A.R. 3-5-2:III and VII)"
Bama had 12 on the field with no one departing.