[just another ref]

This is something I include in the pregame conference every night:

"Coaches, to get in the game, your subs must report to the X. We will work with you if we see your player on his way, but even if you obviously have our attention, he must still touch the X and wait to be beckoned. The horn is not a green light."

Having said all this, this is a call that many officials here simply will not make. I have seen some do everything but tackle the player at the free throw line and drag him back to the X.