Take a good look at your set up. Is there hide outs? Is there multiple levels?
Adding some pallets, placed on saw horses, allows birds to get on top of the pallet or underneath the pallet. Laying a pallet across cement bricks, can give a smaller bird a place where it is harder for other birds to follow. Leaning a piece of plywood, against a wall, allows a bird to get out of sight. Setting up a piece of plywood in the middle of the run to make a mini wall, allows a bird to get out of sight (and out of mind) of the other birds. Place a feeding station behind this wall so that birds eating at the main station, cannot see who is eating behind this one. Adding a roosting bar in the corner of the run is a good idea too. Mine love to perch there and catch the end of the sun in the afternoon.
Make sure that there are two exits from any hide out, so a bird cannot get trapped!
You might take a head count, and measure your set up, might be you are a bit short on space. If you have space, you might pick a middle of the flock bird and confine her with the victim for a while, and then reintroduce them to the flock.
Chasing and pecking have a place in the flock, it determines pecking order, but constant harassment is giving tension to the flock. Sometimes it helps to cull the victim, sometimes it helps to cull the bully, but often it helps to reduce your numbers.
Mrs K