The rule back then had to do with "Defenseless players" and running backs facing up field were not considered defenseless. Also, there was not targeting (head) penalty back then but there was in college. Still, every player understands that its bullshit to try and hit another guy in the helmet at full force like Shitzier did.
And T-Dub, if Shazier doesn't get something for this (games on sofa) then I will become a member of the conspiracy camp.