My $.02... Garrett ripped his helmet off -- way short of kicking a guy in the head while he's got 500 lbs on him.
Garrett flailed at the guy attacking him (yes, Rudolph chose to re-engaged sans helmet) -- again, IMO, way short of Pouncy's deliberate actions.
FWIW, it's important IMO to realize there were TWO events here between Garrett & Rudolph, not just a guy intending to rip someone's helmet off & attack him with it.
I am admittedly colored by my fan-hood and the local interviews with Garrett which show him to be quiet & thoughtful off the field.
I do think your fanhood is coloring your perceptions.
Had the play ended with Garret's tackle of Rudolph it could have, and by recent precedent should have resulted in a flag. The play was over, the ball out, he saw that it was out, and yet he wrestled Rudolph to the ground and was on top of him. Unnecessary to say the least, particularly in that stage of the game. Rudolph was right to take umbrage. Garret was the instigator then of all that followed. At that point Rudolph over reacted. As a leader, as a Q.B. he should have known better, but he didn't. He started struggling, pulling at Garret's helmet and using his leg to try to pry Garret off of him. He did not violently kick Garret or even kick him at all, but no question he had his foot in Garret's groinal region. Then Garret lost his ####, the original instigator, the guy making the unnecessary hit in a game all but over decides to rip the helmet from the guy he originally victimized. Uncalled for. Rudolph then reacted, he charged, a stupid move but given that he did not have his helmet on and Garret did, and Garret now had a weapon there is no reasonable way to say Garret feared Rudolph was going to do anything other than to revile him. He, Garret, was in no danger, reasonably perceived or otherwise. At that point he chose to club Rudolph in the head with sufficient force to make Rudolph's head and neck snap down and back, showing the force. Garret has now asked by every unwritten rule of football, and frankly by the laws of self defense and defense of another to have his force met with equal force or sufficient force to stop the attack. He gets taken to the ground by Decastro. Pouncy sees this and starts circling, so that he, Pouncy, can over-react. While that is going on #65 of the Browns decides to blindside the helmetless victim, a total ##### move and one which ought to have earned him a stomping, but the Steeler nearest backed him down with his mere presence and size. By this time Pouncy has circled around the prostrate Garret. he tries to kick him in the head but misses, instead landing a week kick to the back of another player's leg. Pouncy had intent, but was too inept to complete the act. He then swung and punched at Garret, again a weak attempt, but his intent was there. The intent coupled with the attempt is the offense.
My take, Rudolph is no leader. Garret acted the punk in this instance, a matter that seems out of character and which disappoints me as I own him. He then escalated his bad behavior to a dangerous level. # 65 of the Browns acted the punk and then doubled down by lying in his post game interview, saying he was coming to the aid of his guy, a guy who was the instigator and to whose aid he never came, choosing instead to attack a defenseless man without warning from behind, a totally cowardly act. Pouncy acted a ##### and did so ineptly.
Wow. When I wrote that post, I was thinking that was the perfect situation for Garrett to pull out the race card. There were a couple of PIT linemen there, so it'll be interesting to hear from them (and heck, Pouncey is an African American...didn't seem like he was angry at Rudolph). 
