With no other rooster in the flock, you're it.
Chickens can fight pretty brutally, as we're all aware. Unfortunately, ignoring it is unlikely to resolve the issue.
When I have a mean spirited hen, I dominate them - this means catching and pinning your bird, or tugging their hackles, or poking them between the shoulder blades - none of this is done with the intention to injure, mind you, but with the intention to show them who's in charge using a toned down version of the behavior they show each other. If they escalate, I escalate until they submit.
My hens don't attack me, but I do use this to break up fights during integration and it's very successful.
As I'm now raising roos, I've also picked up a new method for the really unreasonable bird - scoop them up by the legs and hold them out till they calm down and completely relax. - then you can handle or send them on their way. They can't escalate this approach and have no choice but to submit once they realise they aren't going anywhere.
You really only need to do this once or twice to get the point across. I upended one of little roos in the brooder after he started trying to bump me and he did put up a bit if a fight that first time. Second time, he was being a bit too intense and he immediately submitted.without a fight.
Hasn't hurt our relationship. The little guy climbs all over me and wants to be a lap chicken. He also no longer chest bumps or charges me. It's all about communicating with them in a language they understand, though it can look a bit brutal from the outside.