7 week old roosters fighting and drawing blood - argh!

I hatched out 7 adorable bantam naked neck chicks (3 girls and 4 boys) May 8-9.

These little chicks were such cutie pies when they hatched out... but in just a few weeks some of them started becoming aggressive. In the first few weeks I noticed a couple of them had peck marks on them (didn't break the skin)... then a week or so later one of boys had a large bleeding wound on his head. Of course, I separated this boy and he has healed up nicely. I had them in separate quarters for about a week... during this time the rest of the chicks seemed to settle back down and I haven't had another bloody fight issue.
So today I tried to re-introduce separated boy, "Solo", to his hatch mates and this caused an immediate fight - within seconds all 4 boys were fighting each other... the girls all ran away from the fighting. I pulled "Solo" out as quickly as I could and put him back in his separate quarters... he had peck marks on his neck and was bleeding (just a tiny amount) from one of them. I checked the rest of the boys and none of them had any bleeding injuries and they were no longer fighting.
This is the first time I've ever had chicks fight... and I don't mean playful sparring... these guys are seriously fighting and drawing blood.
I am pretty certain that it's not an issue of space / boredom - they have a large shaded coop / pen outside and I rotate their feeders / waterers / dust bath pans / roosting branches / etc.
Also, these boys are different from chicks I've raised in the past as they were pretty easy to sex very early on - very early reddening of combs, wattles - the boys even started practice crowing at 6 (SIX!) weeks!
Has anyone else had anything like this happen? I would love to hear what others have to say... any advice / insight would be most appreciated.
my 3 girls

my 4 boys (second from the left is "Solo")

Do you know which of the bullies is the leader? If so, I would pull him and maybe his first in command out of the brooder and put Solo back in. I had to do this with some older (they were 12 weeks old) bachelors that I have, two would bully a single. I took the bully leader out of the pen for two days, let the bottom and middle bird get to know each other and then put the bully back (course I only had the three). The middle and bottom bird protected each other from the bully (which was the bully's only chance of not getting his head removed earlier than planned).

you can apply rooster booster peck no more, also add grass clippings in there area, Use a red colored light bulb as there light this blends in any blood from wounds which make them less likely to be repecked Chickens are cannibles so first sight of blood can mean more serious wounds . scolding also works sometimes by poking your finger to there beak and telling them no. think of it as bullying the bullies. these are a few things that worked for me hope you find the anwsers your looking for good luck.

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I'm not sure who the leader is... it really happened fast and all 4 of them were fighting. I do think "Solo" is the bottom boy bird though... or maybe he's just the worst fighter in the bunch .
Hmmm... I will try watching them and seeing if I can figure out the hierarchy.
I have thirty something ~11 week old chicks all sharing a pen with absolutely no problems at all. I have boys and girls, different breeds (faverolles, olive eggers, cochins, javas, etc) and different sizes (mostly large fowl and a few bantams) all in there together - they were from 2 different hatches but have been together since they were just a few days old. I guess I really lucked out with those chickies (knocking on wood!) and with my previous hatches... they have all been super easy going and have always gotten along great.
I can't help but think that maybe these Naked Necks boys are somehow more prone to aggressive behavior. They really seem to have developed physically much sooner than any breed I've grown out - combs, wattles, red faces and crowing all before they even turned 6 weeks old. Everything I've read about Naked Necks says they have great temperaments though - super sweet and friendly birds. Maybe it's the ratio... perhaps I have one too many roos tipping the scale.

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I have and use Rooster Booster Peck No More Lotion. I have found it to be a good pecking deterrent and helps the wounds heal. "Solo" took quite awhile to heal... about a week because he was pecked so badly.
I always use a red brooder light... I know white lights can cause issues. I'm not using a red light anymore though... as they are outside now. They have grass and a dusting box in their pen in addition to some other goodies to keep them from getting bored.
Unfortunately, I am not out there with them all the time so I would be unable to scold them for the behavior...