IMHO, it was the ankle that was dirty, I have a strong recollection that there was a "yank" involved at the end of that tackle that wasn't exactly for emphasis. Polltard was looking to put something extra in that awkward takedown
The one that most think was "dirty" wasn't IMHO. When you are around 6' and 200, and see a 6'6 260 lb TE barreling at you, you HAVE to his him low. Either that or get the "fly on the windshield treatment" going high. I've been in that situation and there IS no question.
What was unfortunate was the timing. ACL's are caused in situations like that because the hit occurs EXACTLY at the same moment the cleats are firmly planted in the ground. There is no "give", so bad things happen to the joints. A microsecond earlier or later, with the same hit, and Gronk bounces up and heads back to the huddle.
Sorry Konta, but IIRC there wasn't any chance for a hurdle. I wish there had been, since it would have made any hit one that wouldn't have had his foot firmly planted.