Hi, welcome to the forum. Glad you joined.
I'd keep him separated for a while until you determine what is going on. It is almost certain he is the one doing this. How old is he? How old are the girls. Are the girls laying eggs yet? Their levels of maturity can have a big effect on how they interact. How did you manage the introduction? It's always god information to know what the coop and run look like and their size. In practically any situation the more room they have the better. How many girls?
It sounds like you have an immature cockerel, not a mature rooster. The girls could be immature pullets or more mature hens, but it might help determine what is going on to know which. A good clue to a female's maturity level is whether she is laying or not.
Typically when you introduce a mature rooster to mature hens he impresses them with his self-confidence and magnificence, mates a couple to show he is the boss, and it is over. The flock is his. It's possible that a rooster doesn't have the self-confidence to pull that off and has to resort to brute force to take over the flock. That does not happen often but it can happen. It's also possible that the dominant hen isn't willing to accept a dominant rooster no matter how magnificent he is and resists. It can get kind of violent between the two for a day or two but usually she fairly quickly accepts his dominance. The hens have a part to play in this too, it's not always the rooster.
But if he has hit puberty where the hormones have kicked in telling him to dominate the flock but has not yet reached a mature level, he cannot impress mature hens that he is worthy to dominate them. Immature pullets don't totally understand what is going on but they are probably not going to willingly submit either. When he is immature the mating act is not just about sex but about dominance. The one on bottom is accepting the dominance of the one on top, either willingly or by force. Since they are not willing he resorts to force. And sometime she doesn't even try to mate but just beats them up.
It's not always this bad. Many of us go through this process on a regular basis with few problems. But we are set up for it and have managed it. Even then sometimes it can be hard to watch and we may intervene. With living animals you don't get guarantees as far as behaviors. Each one, male and female, have their own personalities.
The more you can tell us about your situation, flock make-up (ages and numbers), size of your coop and run or other facilities in feet or meters, and what the facilities look like (photos might help) the better we can offer suggestions that for your situation. Basically what do you have to work with?
Now for the head injuries. Part of the mating procedure is the head grab. The one on top grabs the back of the head. This helps balance and position, but it also is the signal for the hen to raise her tail out of the way so the male can hit the target. There will be no fertile eggs without the head grab. In a consensual mating a good technique is to grab some feathers and fairly gently pull. A loose feather might come out but no big deal. But if the mating is by force, it is pretty easy for the comb or even skin to get torn and bleed. Head wounds tend to bleed a lot. That might be what is going on.
When chickens fight they often try to peck the head. They can seriously injure or kill their peck is that strong. It's possible that caused one or both of those head wounds.
There is another factor involved. Chickens can possibly be cannibals. It doesn't happen all the time but your other females might peck at blood or a raw wound. That can kill them. You should monitor those wounded females to make sure your other females aren't attacking them.
I know this is long, hopefully you are not reading it on a tiny hand-held device. But I'll go over one more thing. Why do you want a rooster? What are your goals for that rooster? The only reason you need a rooster is if you want fertile eggs, everything else is personal preference. Preference can be strong, but it is a choice, not a need. I suggest you keep as few roosters as you can and still meet your goals. That's not because you are guaranteed problems with roosters, but the more you have the more likely you are to have problems. I don't know if the right number for you is 0, 1, or more. The more you can tell us about your situation the more likely we can help you meet those goals.
Good luck and once again welcome.
