Player starting to fall in anticipation of charge

[drofficial]

I've heard numerous partners say this type of thing regarding a block/charge situation: If a player is starting to fall/lean back before contact is made, I call that a block."

How does one defend this statement by rule?

If the defender has established legal guarding position and then leans back, starts to fall before contact (into the torso) is made by the offensive player, shouldn't this still be a charge?