The early drive is tied to the word hit, an invented aphorism not in the law book and one which has caused untold confusion and damage. Elite referees claim no hit existed in my day or before the call sequence and they are wrong. What they mean is that there was no engagement and immediate drive and here they are right, that was and still is illegal. It did not happen and does not happen at lower levels because it is penalised. There is no reason to engage as hard as possible as you are either penalised or made to retreat to the mark. Elite packs engage and drive (hit) because they are allowed to, knowing also that they do not have to hook the illegally fed ball. This is a major reason for instability, exacerbated by allowing elite props to bind on the arm and if they do not get it right immediately they collapse.