To be fair, I didn't think it was a penalty at first sight. I thought the defender had just stood his ground. The replay showed differently, the defender did stick his leg out.
Fellaini very lucky, he was retaliating against Huth pulling at his hair, but lashing out like that was OTT. But there's a lot going on out there, I'm rather glad that the referee has decided not to get card-happy. Fascinating game so far.