Having to go for the end zone, Brady stepped up in the pocket, but underthrew a pass to Gronkowski that was easily intercepted by Robert Lester to end the game. However, we had a flag in the end zone as linebacker Luke Kuechly clearly did grab the tight end. The referees talked it over and said there was no penalty and the game was over. The stunning ending drove up the controversy, but the ruling was that the pass was uncatchable, so there cannot be any pass interference.
Now the contact did not happen until the ball was in the air, so there's no illegal contact and there's no defensive holding (Rule 8, Section 4, Article 7). When McCourty was penalized for defensive holding earlier, that contact happened before the ball was even in the air. So it has to be pass interference or nothing, and the referees determined it was uncatchable.
Gronkowski's momentum carried him to the back of the end zone. He made zero effort to come back to the ball. He simply watched the interception unfold. Even if Kuechly did not hug him, the underthrown ball would have forced him to make a cut back to the front of the end zone to have any chance of catching the ball.
Just based on the laws of physics, there's no way Gronkowski could have made this catch, so I agree with the uncatchable ruling, which is a judgment call. Every week there are passes likely impossible to be caught that are deemed catchable, so it's not a ruling referees are consistent on.
However, something still feels shady about the play and what Kuechly did, which was not even necessary as Gronkowski would never get in a position to make the catch.
This ending serves as a reminder that NFL referees are afraid of making critical calls on a late fourth down or on a game-ending play like this. We saw it with the Golden Tate play against Green Bay. Anyone asking for offensive pass interference there is dreaming. In recent history, only the Browns in 2009 against Detroit were penalized for defensive pass interference on a Hail Mary. Referees let guys get away with murder down there.
We saw it in the Super Bowl when there was no call on the Ravens on fourth down for how they defended Michael Crabtree. This is just how the NFL works.
When it comes to referees and critical calls, you live by the sword and you die by the sword. The Patriots should know that as well as any team. Here's Gronkowski pushing off on a fourth-down touchdown against the Giants in 2011:
There's another crucial fourth down with no penalty. Oddly enough, that's the last time Brady suffered a lost comeback (he only has three in his career).