Rooster not aggressive to me but sometimes mean to hens

[MariaChickenMama]

I have a rooster who is 20 months old. He is not aggressive with me. I'm able to come into coop and run and he doesn't attack me.i have seen him not be nice to some of my hens so much that some of my hens rather stay crated up. But I don't want to raise chickens all crated up; I want them to be all together. What would make the rooster do this? And is it possible to train him out of this behavior?

 

[nuthatched]

They aren't part of his harem so he's not sharing resources with them

 

[DobieLover]

I have a rooster who is 20 months old. He is not aggressive with me. I'm able to come into coop and run and he doesn't attack me.i have seen him not be nice to some of my hens so much that some of my hens rather stay crated up. But I don't want to raise chickens all crated up; I want them to be all together. What would make the rooster do this? And is it possible to train him out of this behavior?

Define aggressive.
How long have they been together?
How much space do they have?
How old are the hens?

 

[lagrange chicks]

I had a cockerel that was one of 8 chicks I got last spring, 5 barred rock and 3 easter eggers ( he was a EEer). For reasons un-known he only liked the barred rocks, kept the 2 easter eggers pullets from getting any treats offered. He did mate with the 2 EEers and if I was holding one he would come after me but that was about it, like they weren't part of his flock. Finally I had to cull him, caught him standing on top of one EE pecking her head until bloody. We wish it did not have to end that way as he was are favorite from day 1.

 

[MariaChickenMama]

I had a cockerel that was one of 8 chicks I got last spring, 5 barred rock and 3 easter eggers ( he was a EEer). For reasons un-known he only liked the barred rocks, kept the 2 easter eggers pullets from getting any treats offered. He did mate with the 2 EEers and if I was holding one he would come after me but that was about it, like they weren't part of his flock. Finally I had to cull him, caught him standing on top of one EE pecking her head until bloody. We wish it did not have to end that way as he was are favorite from day 1.

Same. I babied him when he was a chick because I thought everyone was picking on him. At that time I thought he was a hen.

 

[Florida Bullfrog]

Sometimes roosters don't like a hen for breeding reasons. Something about her appearance or behavior tells him she wouldn't be good for him to breed with and therefore she's a waste of resources. It could be an instinctual expression of some sort of detection of ill health, genetic incompatibility (not meaning they can't breed, but that something about the offspring will be less than optimal), or it can simply be his personalty finding her unattractive due to how he was imprinted as a chick.

I have noted that many of my roosters with a high percentage of red junglefowl genetics will reject hens that aren't colored partridge.

 

[SwampPrincessChick]

Sometimes roosters don't like a hen for breeding reasons. Something about her appearance or behavior tells him she wouldn't be good for him to breed with and therefore she's a waste of resources. It could be an instinctual expression of some sort of detection of ill health, genetic incompatibility (not meaning they can't breed, but that something about the offspring will be less than optimal), or it can simply be his personalty finding her unattractive due to how he was imprinted as a chick.

I have noted that many of my roosters with a high percentage of red junglefowl genetics will reject hens that aren't colored partridge.

2x. Roosters can be picky when it comes to who they see as a valuable mate. Males often prefer to breed with hens that have a large comb and large wattles, and a low pecking order status. The former is because it shows that the hen is likely laying a lot of eggs and she has a lot of hormones, and the latter is because it is easier to breed hens who are submissive.

 

[16 and me]

@DobieLover above has some very good questions to consider. Is he harming hens? What kind of behaviours is he showing? Is he new to the flock and trying to establish himself with hens who don't know him, or has he been with them all along? Crowding can be a cause for agressive behaviour, so consider how much space and how many birds you have.
Like @LaGrange, I just recently had to cull a cockerel who cornered a hen and bloodied her eye very badly. He was great with me too, but I noticed he was very dominant with many of the hens. The one he attacked is the more dominant hen, who likely wouldn't submit to him freely, so he beat her into submission.