Thank you for your email.I understand how desperate you are feeling.
Your son is not being naughty. At two-years of age your son is beginning to separate from you and is becoming independent. As he does so he will defy the adults around him, hence the description "The terrible twos." He is also unable to express himself verbally so he does so physically. Understanding this can help you to manage him and I urge you to print my article "Managing two-year-olds" on my website and put it up on your fridge for easy reference.
Knowing that his behaviour is a normal part of toddler development can help you to depersonalise his behaviour and gently guide and manage him, giving him the words to express his feelings. When he becomes angry gently hold him acknowledging his feelings. I can see you are very very angry, you don't want to .... Come let's hit this pillow hard, harder, harder. Do an angry dance. Stomp around the garden, kick the ball as hard as we can. Teach him appropriate ways to express his frustrations, and give him lots of empathy: "I can see you are frustrated and would like to be able to do...Can I help you. Should we try it this way? I understand how you feel."
When he is calm it is important to teach him empathy; putting yourself in someone else's shoes and consider how they are feeling. Empathic people find it very difficult to hurt someone as they know how the victim feels. Use books, opportunities in real life to do this. Obviously if you hit or shout at him, he will role model your behaviour.
Be patient as his vocabulary grows and he becomes more able to do things he will be less defiant. You may also want to read my article titled "Positive Parenting" on my website which gives you guidelines on meeting the needs of children so they are happy and successful.
Good luck and please do not hesitate to contact me again.