[Jim S]

This may be one of the most mis-interpreted rules we have.
The rule is there to do just as it says PREVENT A DIRECT CHARGE INTO THE SNAPPER.
It does not say you can't touch the snapper, it doesn't say the snapper is inviolate for the entire down, it doesn't say that the degree of contact is what is important.
The rule is in place to protect a snapper when he has his head down, looking backwards and his neck is in a vulnerable position. The criteria should be that a defensive player will not charge into the snapper at this time to 1. Cause injury to the snapper. or 2. to knock the snapper out of the way.
Once the snapper has had a chance to recover his position. Ie: get his head back up, this provision no longer applies. However you could still have a personal foul if you thought that a defensive player was 'attacking' the snapper instead of playing to the ball.
If the snapper keeps his head down longer than what is needed to recover the rule no longer applies, and good preventive officiating says we should talk to the snapper. He is leaving himself vulnerable.
If the contact is off to the side by a player attempting to shoot the gap, the rule does not apply. If the contact is because the defender is knocked sideways by the guard (or other), the rule does not apply.
This rule is for a momentary occurance. It's almot like the free blocking zone on this kind of snap, it disappears quickly.
And never tell the defense that they "can't touch the snapper" this isn't true and helps to perpetuate the problem with the understanding of the rule. Tell them not to rough the snappper, or to not run directly into the snapper.