Chi Tang did hit him in retaliation, but what You Yu did counts as self-defense in my book. The dude literally ambushed You Yu when she was alone at night, with clear intention to intimidate/coerce her. Who knows if he could get physical after being told off (see how he forcefully grabbed her last chapter). It it were me, I would scream for help before hitting him.
In the first season it was sad because everyone in the class was like a villain Ì love the little gang they formed this season. All thanks to the class president she is truly grated didnt expect her to be this nice of a character