Over the years I can remember one instance out of so many, where a rooster was actually trying to kill a hen. This particular cockerel would mount and continually peck at the head of the hen as if trying to penetrate the skull. This was not immature happenstance, but extreme aggression. The cockerel was culled and an acceptable one took his place.
Most of the instances of "aggression" I see expressed in these forums is common behavior. It is only the amateur flock raiser that sees the behavior as extreme. They have this idea that chickens are all docile, fuzzy creatures, when they are a survival species with instincts nature gave them, and we know nature can seem quite cruel. Roosters are protective of their flocks and territory. Nature made them tough for a reason. Their instincts should be understood and accepted. Most animals become comfortable with familiarity, so treading gently around more nervous breeds like Leghorns is helpful. Filing spurs to rounded ends should be common practice as to avoid injury to hens in addition to humans. Wear boots and jeans, not sandals and shorts when tending to the flock.
Being able to subdue a rooster without injuring it should be a good practice too, as we should all be handling our birds regularly to check for mites/lice, and overall health. I have seen many instances of housing roosters together, not enough ratio of hens to a rooster, and other common errors people make. Some will argue points simply because they cannot bear being wrong in any instance, but preventing problems reduces stress and promotes health among the flock. It makes raising them more pleasurable too.
