Not really in the mood to argue over this chapter, though I just want to point something out that's been massively overlooked by some of the comments here: You all do realize that the entire reason Rokudou fights is solely to stand up for his friends, right? That's been a consistent theme throughout the entirety of the manga. Even for when he was training (chapter 125), Rokudou would only take his martial arts training seriously when Ling Lan resorted to hurting herself.
Obviously, Rokudou should have stood up for himself and fought the guy off. That point we can all agree on. However, Ranna's intervention was crucial for propelling the plot forward. Whether or not you think that's bad writing on the mangaka's part is up to you. I'm otherwise fine with this setup for the eventual fight between Rokudou and his childhood bully, which I'm sure will be well worth it in the end.