Cats show aggression for many reasons.  One source of aggression can be physical discomfort or pain. The first step to understanding aggression is to rule out any possible medical causes by getting a thorough diagnostic examination with labwork.

Behavioral motivations for aggression include: fear, territory, parental, play, redirected, predatory, petting-induced, pain-induced, social status, medical or learned. Cats may show more than one type of aggression.

Aggression can also be situational or specific to one family member, strangers, other pets in the household, or to unknown pets only.

Keeping a behavioral diary helps identify what causes aggression.

Behavioral treatment usually includes behavior modification techniques, changes to the cat's environment and medical therapy.

Late Socialization: 9 to 16 weeks old[1]:  

• Continues to learn social skills.

• Social play peaks.

• Social conflict over status may emerge.
  

[1] AAFP. (2004). Feline Behavior Guidelines.