wow what a remarkable son you have. Too have kept his cool like that and to defuse such a scary situation with a clear mind. Kudos to him (and to you for raising such a great young man). There isnt a hope in hell that he will be charged, there was no excessive force used, if anything dont be surprised if the police ask if your DS wants to press charges for assult. Huge hugs to you and to your DS, what a scary night.