99.9% sure it was there from birth. It is dark coloured and looks like a blood clot. It is not increasing in size and so is constricting the leg at that point. Not sure but it could be at it's at the leg joint (I'm clued-out in bird anatomy). Bird is favouring the other leg but can put it down and move toes but it's not comfortable doing so, imo. Otherwise a healthy chick. The condition does look similar to another incident on this board where some synthetic fibers got wound around the leg. But this looks definitely like a clot of some sort. Thanks in advance for your help. Daughter is very attached to this one, named Dillweed, after the first got some kinda shock, fell in his water dish and kicked the bucket.