Do you mean your standard-sized chickens are attacking your bantam chickens? You may need to separate your banty, if she's really getting hurt, as opposed to establishing pecking order. Are these all adult chickens? Is the banty one you are trying to introduce to an already established flock? We need a little more information.
shes just a new 3 month old bantam goin in with7 9 week old rhode island reds and 3 laying hens the laying hens protect her but the rhode islands hate her anyone want 7 RIR LOL
I haven't had to do this so I can't give you any good information. I do know that there are lots of threads on here about integrating new birds into your flock. I'd click on the search link in the blue bar at the top and try the word integration and I bet you'll find lots of good advice on here. Good luck!