Bleeding and missing feathers from back of young chicken.

[Brynmckinney67]

Hi everyone, a little over a month ago we got mixed chicks from tractor supply. We recently let them out into the coop with 2 ducks they were raised with and 3 chickens from our last group (2 hens and 1 rooster are left). I do know one hen is being bullied but the other hen is bleeding with this weird brown under her feathers, can anyone help me out here, I don't know what this is

 

[nuthatched]

It's the scab from the tissue where the skins been ripped away.
It might need debriding and antibiotic ointment applied, but I'll let others give you more advice on wound care.