Chicken Behavior

Fights between chickens are somewhat common and are rarely fatal. Almost all chicken fights are caused by dissatisfaction with pecking order rank. In the pecking order of a flock, the higher-ranking birds dominate the middle-ranking birds, who in turn dominate the lower-ranking birds.

When chicks are only a few weeks old they begin fighting with each other to try and determine pecking order rank. This squabbling often continues until they reach maturity and the pecking order has been settled.
Sometimes fights occur among adult birds when a chicken becomes tired of it's position in the pecking order and decides to challenge a higher-ranking bird. More commonly, fights occur when a new bird is introduced to the flock and has to find it's place in the pecking order, or when a bird is re-introduced to the flock after a long absence. Roosters in a fight

Fighting behavior is exhibited by hens and roosters alike; however, rooster fights are more violent and more likely to result in injury or death.

You can often tell when a fight is about to begin by the way two chickens are eyeing each other. They may "casually" circle around each other and pretend to peck at something on the ground while watching their opponent.
When they go face-to-face with each other they will raise their hackles (neck feathers), point their wings towards the ground and spread them apart from their body, stand as tall as they can, and try to face the other chicken down. If neither one "chickens out" at this point, they will start pecking, scratching, jumping at each other, and beating at each other with their wings.

Fatalities can occur when the winner of a fight relentlessly pursues and corners the loser. Fortunately, this is a very infrequent occurrence. Usually it only happens when a lower ranking rooster challenges the top rooster for his position at the head of the flock.