I have a small flock of 6 adult hens 1 adult rir roo. This spring I got a variety of chicks to add to the flock, 1 of the chicks is a Delaware this chick was about 3 mo's old and I introduced her and 3 other chicks to the flock. At first there was a ruckus but they calmed after a while and seemed to be fine in there own group. A couple weeks later I found the delaware chicken laying in the coop with the back of her head and neck area tore open I thought it was the roo trying to mate her. I seperated her for a long time the wound healed nicely. I seperated the roo from the flock to prevent anything else. Yesterday I reintroduced the delaware to the flock, today I came home and the delaware had been attacked again with the same results, since roo was out of the picture it had to be a hen. I let htem all out to free range and watched most of my chickens take turns chasing the delaware chicken, I know have moved back to isolation. What is going on and why?