Hi S.!
I used to know someone whose child did this. She put a helmet on him to protect his head, and then took him to a dr. The boy was ADHD big time!! I'm not suggesting your son is that way. However, I would definately consult your pediatrician for ideas.
Also, I suggest contacting Minirth/Meyer Clinic in Richardson,TX. and see what they suggest. Have you tried restraining him and then praying over him? God does work wonders!! This does work with our 9 yr. old granddaughter when she throws a fit. Speak quietly but firmly. He will quit struggling in order to hear what you have to say. Tell him how much you love him, that God loves him. Tell him that you cannot allow him to act this way. Then start praising God for this child, telling God all his attributes and how much you love this child and how much you love God. KEEP AT IT!! When he quits struggling and after you have prayed over him, place him in time out, face to the wall for about 2 minutes. I promise you, it works.
T.
Good luck! Let us know what worked?