Are there other
chickens in your flock? Is this a male or female?
I'm not terribly familiar with
chickens (I keep mostly ducks), but I know
chickens will exert dominance on other chickens by "hen-picking" them, and removing their feathers as they peck at them. Both roosters and hens can "hen-pick" and be "hen-picked." Sometimes, these sort of dominance issues can be resolved by giving the chickens more space to roam, hiding place, and more things to do. My ducks are always more aggressive with each other when they are stuck in small places, than when they have large areas to roam....