HI kidfarmer, glad you have joined BYC.
Cannot guess what started it, but once there is an injury or red, chicks or chickens will keep pecking. Separation is the first step, if you could do the partition with wire to let them keep seeing but not touching will help avoid reintegration.
Are you using a white or red brooder lamp…if it is white light, then change to the red - it hides red, blood, injury and should help.
I see you have also posted under raising baby chicks. Likely you'll get some experienced input.
Wishing you and all your chicks good luck.