In situations that can make a cat lash out, knowing what to expect, and how to respond, might save you a trip to the doctor.
Redirected aggression. Your cat is in a fight, or he's upset because he can see another cat invading his yard. In such cases, do not touch your cat. He's likely to go after you. "They can stay aroused for a long time," said Nancy Peterson, cat programs manager for the Humane Society of the United States. "I would avoid contact with the cat unless the cat seeks contact with you."
To break up a fight, the best thing to do is distract the cats, giving them a chance to break off the encounter. Spraying water at the aggressor often works. Other options, Peterson said, include clapping your hands loudly or, if the fight is happening indoors, dropping a pillow on the floor next to the cats. Sometimes shaking a bag of treats or opening a can of food is enough distraction.
As a last resort, you can toss a very thick blanket over one of the cats to protect him from the other, but do this only if you can keep your hands out of harm's way.
Play aggression. Your cat bites and scratches while play wrestling with you. This is a sign that the cat is not getting enough play time, and enough play of the right sort.
Cats, especially young ones, need some structured play every day. Kittens need play twice a day for 10 or 15 minutes; for older cats, it depends on their energy levels.
People should never play in a way that puts hands near claws and teeth, even if those little nips seem cute coming from a kitten. Use a wand or other toy. If your cat does bite during play, yell "ouch" and walk away. He'll learn that biting ends the fun. Shouting at him or punishing him will only make him scared and more likely to act out.
Overstimulation. You're petting your cat when he grabs your hand with his mouth. It means he's getting too worked up. "Animals have different tolerances for being petted," Peterson said. Look for signs, such as a twitching tail and ears that have been folded back. Stop immediately. Don't try to shove him off your lap. Stand up to dump him, walk away and leave him alone for a while.
Fear aggression. Never corner a cat. Look for signals: hissing, spitting, growling, crouching, ears flattening. Even rolling on his side can be a sign that he's defensive. "You need to back away. Just get out of his face," Peterson said.
Status-related aggression. You move your cat off the kitchen counter and he swats you. "He's trying to assert himself," Peterson said. Try passive means to discourage the behavior, such as leaving pans of water on the counter so it's not a fun place to sit anymore. You also can try creating an alternative, such as giving him a high perch so that he can be with you, but stay out of the way.
Visit a vet. Finally, if a cat begins showing routine signs of unprovoked aggression, he should be taken to a veterinarian, Peterson said. A wide range of health problems can cause bad behavior.