Having a rooster that is overly aggressive is a problem people commonly face when trying to create or maintain a large flock of chickens. A rooster usually becomes aggressive due to natural instinct. One of a rooster’s primary jobs among a herd is protecting the other chickens. This protective instinct can sometimes get a little out of hand, causing a rooster to become violent. This is usually because the person or animal it is attacking is perceived as a threat (even if they commit no threatening action). Not all roosters necessarily have this problem—many are actually quite gentle.
When dealing with an aggressive rooster, do not let children near it. This can provoke an attack which is likely to harm (and definitely terrify) the child.
One solution many people resort to is separating the rooster from the rest of the flock. This solution has obvious drawbacks, because the rooster is not able to mate with hens or protect the herd. Also, maintaining two separate pens is typically more of a hassle than maintaining just one.
Another solution is to confront the rooster. A rooster may attack you because he sees you as occupying a lower place on the pecking order. You need to get to the top—become the ‘Alpha Rooster’. One way to do this is to pick up the rooster and hold him steady, no matter what he does. Hold him there until he has been calm for 15 to 30 minutes. Then set him down. If, as you set him down, he resumes fighting, pick him back up and repeat the process. Do this every time he is hostile. If he ever tries to bite you, hold his beak shut for a moment, until he remembers who is boss. You may need to continue to do this procedure every day for several weeks.
Confronting the Rooster
Some people also recommend not allowing the problem rooster to mate with any of the hens in your presence, as he may be doing this to show superiority.
A rooster is more likely to be calm if it is trained from a young age. Most problems people report occur after the rooster switches owners, especially from a less competent owner.
It is also important to remember that, in most cases, the quality that causes the rooster to attack or be otherwise aggressive is a good one. This is the quality that will motivate your rooster to fight to protect the rest of the flock and defend them from predators. Most roosters will fight to the death to prevent any harm to the flock.
For extremely aggressive roosters (or after an especially violent episode) more drastic measures may be needed.
For more information, http://www.backyardchickens.com/a/dealing-with-roosters-roo-behavior may be a useful web page.