No, the coaches do not NEED to be in that area. They are the only people ALLOWED in that area. Those are two very different statements. Practice squad players are not allowed (and were) in there. The coaches have the obligation to get out of the way of a player blocked out of bounds. The wall is specifically illegal because it was there for the purpose of changing where the player could run. The rules specifically state that any impeding of a player's motion by a substitute or coach is a 15 yard unsportsmanlike penalty. This was a premeditated penalty committed by the coaches.