Ever see roosters fight? Kicking, chest butting, screaming, grabbing at feathers and tearing just like sharks do. Its a full bite with shaking, the intent to tear.
Ill try to get pictures when i get home. Right now my son is babysitting trying to keep them apart.
One thing he observed is they seem to want to chase the others away from the warmth and light.
All thr chicks are under 2 weeks old.
None of them has had any meat or contact with injured chicks. They leave the day olds alone.
Interesting about chasing from the light. It could be territorial behavior, but check your brooder temperature nonetheless.
Chicks do fight/posture/chest bump, etc., to establish the pecking order, both pullets and cockerels do this, so gender is not necessarily the problem. Yes, even this young of an age pecking order is already in full swing. These 3 are making sure everyone knows that they are top tier chicks (for now).
This continues all throughout their whole lives. A lot depends on the personality of the chickens and possibly breed, but even adults show some type of dominance to one another on a daily basis. If you have an established flock, watch your top hen, she does "rule" somehow, it can be a stare down/stink eye, peck, whine or flogging if necessary- sometimes it's so subtle that you may not even know what she's doing, but it's there. I am no expert on behavior, I'm still learning and have made mistakes, but it's very interesting just to sit or stand out of the way inside the run, let them go about their business and observe, each member of the flock knows their place, but still occasionally tests the waters, there is always another hen looking to move up the chicken ladder.
Pecking order can seem very brutal at times, but such is the culture of chickens. If no blood is being drawn, then it may be better to let it play out. Chickens can be dramatic, they act and sound like they are being shredded to pieces and dying. If you keep intervening, the battle continues. If blood is being drawn, then intervention would be needed.
Having plenty of space always helps, if there is room, put a few obstacles in the brooder to break up line of vision.
Just my thoughts.