Sometimes a specific rooster is just too aggressive as a breeder. I have a huge rooster that daily breeds with a bantam sized hen and there is no issue, because he is gentle...Apparently very gentle...I have 2 adult roosters, but only 3 hens that are laying. Only the large rooster is successfully breeding any of the hens though, because he literally spends all his time making sure that the smaller rooster is not breeding any of them...Lol. We have 4 pullets getting ready to start laying...and I will be ordering a lot of chicks for the spring.
Younger roosters are harder on hens than an older larger roo as well. So how old is your rooster?