It seems there is a lot of confusion and lack of clear understanding on the "unnecessary roughness" penalty currently in effect. After further review, I can understand a lot of the confusion. After doing some Google sleuthing, I came to realize that the NFL might be the only pro sport who doesn't provide an official rule-book online. They conveniently charge for it. Well, $10 later I'm here to shine a light on the subject!

Here are the excerpts regarding the "Unnecessary Roughness" and "Defenseless Player" rules. I bolded the parts directly pertaining to the controversial Rahim Moore hit.

---Rule 12, Section 2, Article 8 "Unnecessary Roughness":

There shall be no unnecessary roughness. This shall include, but will not be limited to:

(a) striking an opponent anywhere with the foot or any part of the leg with a whipping motion;

(b) contacting a runner out of bounds:

(c) a member of the receiving team cannot go out of bounds and contact a kicking team player out of

     bounds. If this occurs on a kick from scrimmage, post-possession rules would apply if appropriate (9-

     5-1);

(d) running or diving into, or throwing the body against or on a ball carrier who falls or slips to the ground

      untouched and makes no attempt to advance, before or after the ball is dead;

(e) unnecessarily running, diving into, cutting, or throwing the body against or on a player who (i) is out of

      the play or (ii) should not have reasonably anticipated such contact by an opponent, before or after

      the ball is dead; or throwing the runner to the ground after the ball is dead;

(f)  a kicker/punter, who is standing still or fading backwards after the ball has been kicked, is out of the

     play and must not be unnecessarily contacted by the receiving team through the end of the play or

     until he assumes a distinctly defensive position.

(g) If a player uses any part of his helmet (including the top/crown and forehead/"hairline" parts) or

     facemask to butt, spear, or ram an opponent violently or unnecessarily.

(h) any player who grabs a helmet opening of an opponent and forcibly twists, turns, or pulls his head.

(i) Illegal contact with the helmet against the knee of the snapper during an attempt for a field goal or

    kick try.

(j) if a player illegally launches into a defenseless opponent. It is an illegal launch if a player (1) leaves

    both feet prior to contact to spring forward and upward into his opponent, and (2) uses any part of his

    helmet (including the top/crown and forehead/"hairline" parts) to initiate forcible contact against any

    part of his opponent’s body.

 

Note: This does not apply to contact against a runner, unless the runner is still considered to be adefenseless

player, as defined in Rule 12, Section 2, Article 9.

 

 

---Rule 12, Section 2, Article 9 "Defenseless Player":

It is a foul if a player initiates unnecessary contact against a player who is in a defenseless posture. (a) Players in a defenseless posture are:    

(1) A player in the act of or just after throwing a pass;    

(2) A receiver attempting to catch a pass; or who has completed a catch and has not had time to protect himself or has not clearly become a runner. If the receiver/runner is capable of avoiding or warding off the impending contact of an opponent, he is no longer a defenseless player;    

(3) A runner already in the grasp of a tackler and whose forward progress has been stopped;    

(4) A kickoff or punt returner attempting to field a kick in the air;    

(5) A player on the ground at the end of a play;    

(6) A kicker/punter during the kick or during the return;    

(7) A quarterback at any time after a change of possession, and    

(8) A player who receives a "blindside" block when the blocker is moving toward his own endline and           approaches the opponent from behind or from the side.

(b) Prohibited contact against a player who is in a defenseless posture is:    

(1) Forcibly hitting the defenseless player’s head or neck area with the helmet, facemask, forearm, or               shoulder, regardless of whether the defensive player also uses his arms to tackle the defenseless player by encircling or grasping him; and    

(2) Lowering the head and making forcible contact with the top/crown or forehead/"hairline" parts of the helmet against any part of the defenseless player’s body.                              

Note: The provisions of (2) do not prohibit incidental contact by the mask or helmet in the course of a
          conventional tackle on an opponent.

Going back to the Rahim Moore hit. I've been of the belief that it was a borderline, but completely legal hit on a defenseless receiver. After reading the official rule a little closer, I now think the officials made the correct call.
I believe what makes Moore's hit illegal wasn't contact to the receiver's head, as I originally thought they flagged him for. What makes his hit illegal is tucked away in Article 9, b, 1.

Forcibly hitting the defenseless player's head or neck area... 

I thought the hit was completely legal due to it being a shoulder to upper chest hit. Well, I'm pretty sure most people can agree that upper chest can also be described as "neck area."
It looks like the league made the correct call. As for the fine; I can't say, but by the rule of law Rahim's hit was illegal.