Fortunately, most cats in a household are pleasant family members. They get along with their humans and other "relatives." But there are times when two cats will have a "dog fight,"but any aggression should be confronted immediately. Cats' teeth and claws can inflict serious damage.

Cat aggression can be classified as folows: intermale, territorial, fear-induced, orplay.
Raging hormones are responsible for the growling, howling, and posturing common to intact (uncastrated) tom cats trying to hold on to their territory and girl friends. Castration will stop this behavior.
Cat Aggresssion TreatmentIf you have a cat that is always a victimof another cat's hissing, growling, chasing, biting and scratching, and only comes out of hiding when the other cat is not around, you may want to give the aggressive cat access to the outdoors or restrict the cats involved to separate areas of the house so they do not encounter each other. This should stop territorial aggression. If not, find one of the cats a new home (without other cats).