[Steve_Seattle]

"Except it was an obviously catchable ball"

It was not obviously catchable except by the guy who intercepted it. Gronkowski was about five yards past the ball, and his momentum was carrying him away from the ball even without the interference. I am not a rules expert, but you can argue that it was not pass interference because Gronkowski almost certainly could not have caught the pass - he would have had to go through the defender to get it (the pass was low, not one that Gronkowski could have used his height advantage on).

But holding is another thing - Gronkowski was clearly held - and in that case it might not matter whether the ball was catchable or not.

[Labyrinthos]

It was not obviously catchable except by the guy who intercepted it.

It was arguably catchable to the referee who immediately threw the flag otherwise he never would have thrown the flag in the first place.

[9YearLurker]

You can’t say it wasn’t pass interference because the guy couldn’t have caught the pass—because of the interference!