Even baby chicks will sometimes pick on each other, and sometimes what looks like picking on or bullying is just exploring and learning. They're learning about the world around them, what's what, and how to be chickens really, haha. Make sure the brooder has enough space, and plenty of things to occupy their attention. Making little roosts and ladders, randomly chucking some food (chick starter, small amounts of oats, or other dry stuff) around the bedding gives them something to forage for and entertains them. I chucked a couple of cardboard toilet rolls and paper towels into the brooder, they just loved scratching up and ripping apart the paper towels, and would push around, try to get into and on top of the toilet rolls - Very cute to watch. I've also tried hanging a strawberry and slices of apple from a string across the top of the brooder so that it hung down into the middle of their play area. Some loved jumping up and climbing on things to peck away at the treat, others were scared by something hanging above them. I think that instinct to be afraid of shadows and things above them is quite strong in young chicks. Generally I've heard the conventional wisdom is that if there's any blood, you need to act, remove the bully and treat the victim. But unless there's any actual damage being done (so yes, blood, but also broken beaks or nostrils, bald patches from feather pecking, not being allowed access to food, water, or the warm spots under the heat lamps) you usually just let them sort it out. Putting in 2 feeders and waterers might help too, as they won't feel as though they're competing for resources and that getting territorial.
