At this age, alongside other elements, aggression also comes to play in your child. Hence, he learns about physical violence. Handling his temper and teaching him how to manage his anger is a very sensitive issue, which requires careful and sensitive handling.
What you need to know
Some parents are under the impression that if the child is allowed to express his anger by beating a pillow or even his mother, he will be pacified. This is completely wrong. You must teach your child not to express his anger through violence. A child who is allowed to do so will inevitably grow up to be a violent person. Restrain your child when he is angry and prevent him from committing any physical violence. Tell him that you understand he is angry, and talk to him about how to address the issue. Make him understand that it is always better to express anger verbally by talking it out.
What you need to do
Tell your child that you understand that he is angry and that being angry is not wrong. But expressing anger physically is not right. This is the appropriate age to do teach your child to control his emotions and manage his temper. As far as possible try to preempt or avoid situations which lead to such behaviour.