I would caution coaches to be very careful in correcting hitters who they believe are pulling their heads off the ball. If the batter is stepping in the bucket or is falling away from the plate, then he obviously has a problem that needs correcting. But in many cases the problem appears to be that the batter is turning his head and taking his eyes off the ball before contact. --- Here is where I advise a lot of caution before messing with a player's mechanics.
When I was coaching, I, like most coaches, considered pulling the head off the ball to be a problem that effected many of the young hitters. I recorded the swings of hundreds of high school and college players, and what I found while reviewing those swings in frame-by-frame action was very surprising. I discovered that very, very few hitters were pulling their heads out before the bat passed through the contact zone. Yes, their heads were being pulled out but it happened later during the swing's follow-through.
I can fully understand why many coaches might disagree. It certainly does appear that hitters are pulling their heads out before contact. But we must remember that the entire swing takes less than a half of a second. The time from contact to follow-through is about 1/30 of a second. Our eye reflexes are just not fast enough to clearly see the difference in head movement between contact and follow-through.
I have seen (and heard) on video many coaches yelling at their hitters that they are pulling their heads out. When I reviewed the swings frame-by-frame, the players head and eyes were just fine through contact --- it was the back shoulder being pulled through by the reaction of the bat during follow-through that forced the hitters head out. --- In most cases, if the batter is told he is pulling his head out, he will try to correct his "non-problem" by slowing his bodies rotation and relying more on his arms to swing with. ---