User blog comment:IamJakuhoRaikoben/Chapter 355: Song of the Fairies, Review./@comment-5006572-20131010190448/@comment-5580383-20131011010126

" why Erza wasnt able to defends herself from stupid raging Natsu."

Cuz she was caught offguard and was enjoying the touch of Natsu, as you see, she gets back up and kicks his ass  as usual. BTW, that bastard was lucky to be behind Erza.