That challenge from Azcipuelcta was 100% red card, absolute shocker and to make it worse Frankfurt had a promising attack and the referee pulled it back without playing advantage, once he pulled it back i was sure he was going to issue the red card.
I'm not so sure. I have to say that when I saw it in real time, my first instinct was red but then the replays showed that Azpilicueta saw what was happening and was still in enough control to pull his foot away and in the end made no more than minimal contact with the opponent. The referee apparently saw it that way that too and (I think) judged correctly that the tackle while reckless, did not use excessive force, nor did it endanger the safety of the opponent.
Azpi is off for me there, shocking challenge and no idea why the ref pulled it back instead of allowing advantage. Thought he'd give the red the moment he blew the whistle and am still surprised he didn't.