The non-call in the Ratbirds 2014 playoff game was one of those muggings. It's a big 3rd down play with the Pats trailling, the ball is thrown to Gronk in the middle of the field where everyone can see (even the refs), TB12 has it right on the money (what else?), Gronk has his body between the pass and the LB trying to cover him, but then Gronk can't raise his arms because the defender clearly has them both pinned down to his side. Time for the Pats to punt.
Another non call was the HUGE one at the end of a game in Charlotte a few years ago. That was a play where the defender simply tackled Gronk while the ball was on the way so he couldn't move to get it. That one cost the Pats the game.
We could probably start a thread here about the poor calls and non-calls against Gronk.