I live on a huge farm. My chickens free range around and they definitely have enough space so that is not the reason why that rooster killed the chick. He tried to mate the hen hen then stepped on the chick and killed it! But I anyway sold him because he was harassing the hens and they lost all their feathers on their backs!I have never had a mature rooster try to kill chicks. I have had a very large number of roosters. Very definitely reconsider your husbandry techniques and adjust those if a rooster or especially roosters are even aggressive towards chicks.