3 week old roo going after other chicks

[FrahmChicks217]

So what e a couple of roos. So far for sure 2, both brown leghorns. One though I noticed today is going after 2 other chicks. There are 28 in total that are 3 weeks old. I'm just trying to figure out if this behavior is normal or if I need to rehome him. I do know more then likely I'll have to rehome some to keep the rooster to ĥen ratio in check and I have 10 easter eggers that I won't know what they are till the are older. He is hopping onto their backs and grabbing the feathers/fluff of the back of their necks. The funny thing is, is these 2 chicks are bigger then him. They are around 5 days older then he is. But I only see him doing this and not my other confirmed roo. Thanks for any advise

Pic of naughty roo.

 

[red horse ranch]

The only brown Leghorn roos I ever had were both extremely aggressive and ended up in the fry pan!

 

[LaFleche]

How much space do they have and what is the temperature in their brooder?
Do they have entertainment like dust bath, roosts to climb on or clumps of grass and soil to scratch around in?
A picture of the brooder would help.