That cat you took in off the street used to be the very image of sweetness. He seemed so genuinely grateful to be in a safe, warm home, but recently he has become aggressive. Perhaps he swipes at you with his claws or bites, or perhaps he has begun fighting with other pets. Maybe he has begun attacking you in bed. What could be the cause of the sudden reversal?
Cats can exhibit aggressive behavior for a number of reasons. Some of what you see as aggression may even be what your cat considers play. Cats rarely have a different way of playing with humans than they do for other cats.
Too Much Petting
Most cats love to be petted when you spend time with them, but they also have limits. If you touch a cat somewhere that it doesn't like to be touched, it may decide that petting time is over. Sometimes when the cat's mood swing and does not want to be pet anymore, his purring will stop and out comes the little claws and teeth. This is normal behavior in most cats and the only way to get around this is to understand and read your cat's body language better.
Play Aggression
The predator lurking within your cat occasionally comes out, and often when you are not expecting it. A cat in the wild stalks and pounces on its prey, and you may find that that arm that's dangling off of the couch or that foot that has sneaked out from under the blanket suddenly becomes the new target of your cat's favorite play hunt. Your cat might also like to hide in certain corners of your house and pounce on you when you walk past. This is all in play, and your cat certainly doesn't intend to do you harm.
Fear and Defense
It's very important for a new cat owner to properly socialize their animal. A cat needs to feel comfortable and safe around people. Cats, unlike many canines, will often fight instead of running away from a perceived danger. If your cat is fearful, it may lash out at you. The best way to get around this is simply to remove the thing your cat fears. Otherwise, enticing your cat with a wonderful treat like tuna might get him to slowly conquer his fear.
The Wrong Target
Cats can be very moody, and if something irritates or agitates them, they can stay in that state for hours, even as long as a day. If your cat is frustrated by a cat or a bird outside the window, he might show his frustration at you or anyone who happens to be near him. If you can sense that your cat is agitated, leave her alone first and remove the source of agitation. For example, you can close the curtains.
Cat Fights
Cats will sometimes fight with other cats. Being territorial animals by nature, and generally solitary, a cat might see another cat in the yard as an act of war. It is very difficult to teach your cat not to do this; the only solution is to either keep the other cat away from yours or vice versa.
At times, two cats who have been getting along well will also get into a fight. These bouts of aggression could be the result of just about anything at all. Treats and love may be your only hope of reconciling their differences, and they may simply need some time apart.