This same exact thing literally happened to me... My chickens attacked my bantam and Araucana. I don't know why they are so rude to them. Make sure to get the blood off of the Araucana because chickens are attracted to blood. I recommend treating the bare, bloody spot. My chickens are still attacking the two hens and we have already had one die. I feel like I am out of options since I have added new things into the run for boredom. I am so sorry, and I don't know how to help since I need help to.