This article analyses the place of the intersections of the criminal law of assault and the Family Court's welfare jurisdiction in rendering Family Court authorised sterilisation of girls with intellectual disability a legally permissible form of violence. The article does this by examining court authorised sterilisation of girls with intellectual disability by reference to the concepts of 'legal violence' and 'abnormality'. The article's central argument is that Family Court authorised sterilisation of girls with intellectual disability is a form of lawful and 'good' violence against abnormal legal subjects. Such girls are - by reason of their incapacity - positioned outside the group of 'normal' legal subjects of assault who have the capacity to decide to consent to contact with their otherwise 'impermeable' and legally sacrosanct bodies. As the girls with intellectual disability are deemed to constitute 'abnormal' legal subjects of assault, the lawfulness of the contact involved in the act of their sterilisation is not dependent on the consent of the girls themselves, but instead on the consent of their parents as authorised by the Family Court acting in its welfare jurisdiction. In the course of authorising parental consent to sterilisation, the Family Court not only renders an act of sterilisation 'lawful violence', but also 'good violence' through the characterisation of girls with intellectual disability as absolutely different to individuals without disability, and through the characterisation of the act in legal, familial and medical terms.