I've had a few polish and luckily only experienced this with one rooster--the poor boy let the girls pick on him like such a gentleman, but a stupid gentleman at that. For some reason I was lucky and the females never got more than a few snags on the head during integration, with no 'crest-targeting' in their adult age.
So I'm not extremely experienced but I know what it looks like and how it happened to mine. I've gone through many, many different periods where every hen has their rump feathers picked out by each other, or periods where they pick out any beards the bearded girls have, or times when the chest is pecked clean by boredom. The less likely solution that I think helped with me was moving them to a larger run--so they had more to do and were less bored/interested in each other--and get them out free ranging. Essentially, I had to give the picked-on girls or my polish roo a break. But specifically on my little polish roo....he was never fully-crested--the girls picked him clean seemingly as a new crest came in. But I think it was partially his fault because he just submitted to them and the hens liked being around him.
Because blood is so attractive, I would suggest separating temporarily until the crest comes back in/heals. With feathers instead of bloody scalp, the head will become less interesting--but this might not solve the issue completely. Providing entertaining of some kind, like the foam mentioned by Lolly above, can help make other activities/peck-able things more enticing than your poor birds' scalps.
