Please consult a child psychologist near you asap. There may be many reasons for such behavior - anxiety problems, misbehavior by someone at school , might even be sexual or physical abuse.
Children are able to share such with trained mental health professionals even if they find it difficult to do so with parents, so you should make best use of it.
Even if it's not something as severe, a child psychologist or child psychiatrist shall be able to guide both yourself and your child to be able to address this issue much effectively.
Next Steps
in the meanwhile, provide him with as much love and support as you can, try not to be angry or violent. remember, children need love the most, when they least deserve it. good luck!
Health Tips
kindly seek professional help urgently.