Blackmail is an act of coercion using the threat of revealing or publicizing either substantially true or false information about a person or people unless certain demands are met. It is often damaging information, and may be revealed to family members or associates rather than to the general public. It may involve using threats of physical, mental or emotional harm, or of criminal prosecution, against the victim or someone close to the victim.
Black mailing is not allowed in Islam. Asking money from people must be based on lawful contract i.e. selling , renting, etc. As he did not commit the crime, you can not ask him for money just for trying to harm you. Such money will be illegal money.
If he hit you causing reddishness on your body or more effect, then you will be entitled to take penalty ( Diyyah) from him. The penalty amount depends on the extend of the harm on your body caused directly by him.