The defenseless player is the concept of the day.
“It is a foul if a player initiates unnecessary contact against a player who is in a defenseless posture.”
To simplify it, it is a hit against a player that is unable to protect or defend himself.
It’s dirty, it’s illegal and you certainly hate seeing it happen to one of your players like below. Some would call it head-hunting.
It is a staple of Dirty Ass Gregg Williams’ defenses, again, shown above.
Many argued that this hit was clean, because it was shoulder to shoulder. While that may be true, Sanders was also in a defenseless position and going for the ball which is his right. McLeod was not. He was going for Sanders head and just missed. He was flagged but wasn’t fined. With Sanders stretching/diving for the ball he was in no way shape or form able to protect himself from the impending contact.
Another example is this hit on Wes Welker by the Seattle Seahawks:
This is easily head-hunting.
With Welker looking back for the ball he was in no way shape or form able to protect himself from the impending contact. It was away from the play.
The NFL Video Rulebook has the Welker play as one of their examples.
They label it as a foul, yet but Bill Vinovich (imagine that) and his backjudge (Jim Quirk) failed to call a penalty. The INT was returned 52 yards, and set up a short FG to give Seattle a 20-12 lead with a minute to go. Peyton Manning and company orchestrated a 6 play 81 yard drive in 0:41 which was capped off with a Jacob Tamme 26 yard td catch and then a Manning to Demaryius Thomas 2-point-conversion, but the missed penalty was a game changer. Had they thrown the obvious flag, it would have been 1&10 Denver at the 12 with about 2:20 left down 17-12. Game changer.