I don't know how it started, but I know how it ended. I went outside to show my daughter and granddaughter then new babies and there was trouble in the big girl pen. I thought at first that my Roo was just mating, then I saw he was getting very aggressive which is so unlike him. Then 4 more hens joined in and the wounded one was trying to escape, there was blood and she was limping. I ran in and was able to catch her and get her out. There was blood dripping off her beak, yet I could not find the source of the wound. There is a small wound on her comb (she's a White Leghorn) but it was not bleeding very much. I put her in the quaranteen pen and she is resting well right now. I could not see why she was limping, but I'll keep an eye on her. Now, after all that, when she gets better, can she go back into the pen with the others, or will they continue to pick on her. This is the first time anything like this has happened. I have 2 more pens, both younger then the one she was in. Any help would be great, I don't want to get her well, then put her back and have her hurt again. I know how chickens get when they see blood, I just wish I knew how and why it started.