Growth/pimple on skin of chicken

Hello chicken lovers,
One of my hens has growth/pimple on the skin.
The hen does appear to peck near the growth but not the growth itself and not all the time, just occasionally.
I have attached a photo (hopefully), although it is not a good one as the hen (Ginger) does flinch when I move the feathers to get thephoto but, does not flinch when I move the wing feathers.
I guess it is either sore or tender around the area.
Also some damage has been done since I first noticed the growth (two weeks ago?) by a fox attack.
So she has lost some feathers from the fox attack.

Hello ghost61,
Thank you for that info.
Yes, it is near the tail feathers.
I've learnt a bit more and can stop worrying.
What is though? Any idea?

Hello Snow White,
Thank you for the reply.
That explains why I see the hens preening near their rear then somewhere else soon after.