If your cat is pouncing on your ankles as you pass by,  he’s probably trying to act on his instinct to hunt prey.  Try to anticipate this and redirect his frenzy to a cat toy on a stick or even a rolling toy. When your cat goes for your ankles, clap your hands or stomp your foot to cut it short.  Indoor cats need lots of active and interactive play. If you offer him some indoor exercise and play on a daily basis this problem may be cured.  The assault on your ankles usually takes place when your cat is a kitten and stops as soon as he gets older. If your cat launches a serious attack that breaks your skin, take him to the veterinarian. The aggression might be caused by pain, a hormonal change or a nervous system problem.