I don't understand why the runner is fully allowed to lower his head into hits but the defender isn't allowed to do the same. The way targeting is ruled, the offensive player's safety is placed entirely in the hands of the defender.
I still remember the goalline play against Alabama a few years back when Daniel Bituli was ejected for targeting... on a play where the hit occurred about a foot and a half off the grass. An offensive player dives headfirst, and somehow the defender is expected to adjust to that in real time? Come on now.