No it wasn't
Apart from the fella lying defenceless on the floor
Not getting a blatant call is no excuse for basically attacking someone when the play is dead.
They should have thrown the book at Gronk. The game had stopped. He made a conscious decision to do what he did. It's not like a split second decision on the field when the ball was alive.
I suspect the NFL don't want to be seen as a bunch of fannies and therefore didn't make an example of him. Any other sport he'd be looking at more than a 1 game ban for the same offence.
No chance the league was going to make an example of a Pats player after the whole Deflategate saga. Fully agree that Gronkowski acted like an utter c*nt and that they should've thrown the book at him. Same for Kiko Alonso on Flacco or Trevathan on Adams earlier in the year. Banned for the rest of the season or something to that extent.
The game itself is prone to unavoidable injuries, deliberately dirty or gratuitous hits, especially targeting the head, should not be tolerated in any way and punished with the maximum severity.
Anyway, "thanks" to the above poster for highlighting how much the fans and the culture around the sport are a big part of the problem.