Try to think this through for a minute. Where does Daryl come from? A very poor area. How long has he been abused like that? Probably since he was a kid. If he was abused since he was a kid could it be he didn't get enough to eat? Seems to be very likely. Would he then really be able to give a real fight? Nope. He wouldn't. On top of that, how much self confidence would someone who has been abused since small have? Close to zero.
Even if he did punch Ren, it would cause more problems than solving them. After all, Ren is a nobleman, and back in the day if you had a servant that would dare to harm you, the servant would most likely be killed...same with his mother's lover, even if he did punch that guy, there is no way he could overpower him. The guy would probably kill him. After all, the reason he ran away was because the abuse was already escalating to a dangerous level
Daryl is man, right? but why he so weak than woman? (woman now a day know how to punch) Daryl and Ren has same tall right but why Daryl doesn't dare to punch when Ren try to do him same as he doesn't dare to punch his mother lover. Is Daryl got beaten or sexual abuse or both that he ran away from house. What about Daryl relationship with his mother is good or bad but from Daryl look his mother probably don't care about him. Ren save Daryl that why Daryl let Ren do him after Ren said he will not hurt Daryl so Daryl trust Ren and he become Ren lover and servant to.