This is why he decided to stop sleeping in the coop. This does not always happen, but sometimes when the hormones hit an immature cockerel a mature hen will attack him. It may be just one hen, it may be several mature hens. It is often the dominant hen but not always.
Some mature hens will accept the advances of about anything in spurs or that will eventually have spurs, though 10 weeks is not likely. That's really young, it's usually closer to 15 weeks before this happens. But many, let's say most, mature hens expect the potential father of their children to behave like a responsible father. An immature cockerel can't meet that standard so they don't let him mate them. Often they just run away but occasionally one or some fight back when he bothers them. There might be some of that going on. But that's a reaction, not an aggression on the hen's part. That doesn't sound quite like what you are seeing since he is being attacked as he enters the coop.
Sometimes the hens see an immature cockerel as a threat to their dominant position. At some point he will mature to the point that he will become flock master so they are brutal to him, keeping him down in the pecking order as low as they can for as long as they can. Often it is the dominant hen that does this. I think this is mainly what is going on. He has revealed himself to be male so the dominant hen is keeping him down as long as she can. Some people like to see this. They consider this "schooling" him, teaching him to properly respect hens. I consider it just typical chicken behavior as some go through puberty.
You can often see some of this behavior if you are integrating young pullets into a flock of mature hens. Sometimes the adults peck or attack the pullets as they are trying to settle down for the night. My coop is big enough that they can usually find a safe place to sleep where the adults don't bother them but occasionally I'll have a group of teenagers stop sleeping in the coop. Mine are restricted to a run so they aren't that hard to catch after dark so I just toss them into the coop and lock them in there. It may take a while but they eventually get the message. Having extra room in the coop helps.
I don't know what your coop looks like or how well he can enter and find a safe place to sleep where she doesn't attack him. That may complicate this some for you. At some point, if he survives, he will mature to the point that he takes over but that could be several months down the road. They may reach some accommodation before that and the violence stop. You never know how these things will play out.
My suggestion is the same as it usually is in this type of situation. Keep an eye on it and base your actions on what you see, not what some stranger over the internet like me tells you that you will see. Each situation is unique, you never know for sure what will happen. As long as none are getting injured try to let them work it out. Have a Plan B, some place you can isolate a chicken in a moment's notice in case it becomes necessary. A wire dog cage or even a plastic crate can work in an emergency. Good luck!
At the same time this change occurred, he started roosting in our tree beside the coop, instead of in the coop with the hens. I've climbed up and gotten him down 4 or 5 times and put him in the coop, but he keeps going up there! What's the deal? Thoughts/advice?
