[FredZarguna]

Yes, and the key word is “defenseless.” If he has secured the ball and made a “football move” which includes taking two or more steps, he is subject to the same rules as a running back. Burfict and Jones both made hits on defenseless receivers. Shazier did NOT. That’s the whole difference.

[grateful]

The rules have changed.

ARTICLE 8. INITIATING CONTACT WITH THE CROWN OF THE HELMET
It is a foul if a runner or tackler initiates forcible contact by delivering a blow with the top/crown of his helmet against an opponent when both players are clearly outside the tackle box (an area extending from tackle to tackle and from three yards beyond the line of scrimmage to the offensive team's end line).

Whether he's a defenseless receiver or a runner is irrelevant now. Current NFL rules call this an illegal hit.