Honestly, every one screwed up, it's just varying degrees of screw up.
Rudolph started going too far with the (apparent) groin shot to Garrett.
Garrett responded with tearing off Rudolph's helmet.
DeCastro intelligently steps between Rudolph and Garrett.
At this point, both have made mistakes, but nothing particularly bad. 15 yard penalty on Garrett and a likely fine.
And then it goes off the rails.
With his linemen protecting him (3 vs. 1), Rudolph goes after Garrett.
Garrett swings the haymaker with the helmet.
Pouncey intervenes (I'm okay with this move)
Pouncey kicks Garrett while he's on the ground (not okay with this one).
If I'm the commish, I'm dropping crap on all them:
1. Garrett gets 16 games. However we ended up here, this is assault with a weapon.
2. Pouncey gets 2-4 games. Once his quarterback was safe, he's immediate in the wrong to continue.
3. Rudolph gets 2 games. 1 game for starting this pissing match, 1 game to keep him from playing the Browns in 2 weeks. He gets sacrificed to keep himself safe AND to prevent the rematch from devolving into a complete brawl at the coin toss.
A significant part of this is to make an example out of everyone. All three parties screwed up bad. Some just worse than others.
As an aside, Garrett should be charged with (assault? battery?). This is not within the rules of the game. He used a weapon to attack someone. If he is charged, I expect him to be convicted/plead guilty.