The law does not permit the assault on the boy that took place here. The fact of the father's outrage does not change that. Even where things like this go unpunished, it is only because the the authorities decline to enforce the law as it stands.

As Christians we are to submit to the secular authority where it does not require us to disobey God. God does not require us to beat up the boyfriend that is trying (with however much success) to seduce our daughter. "We gave no such command." Therefore, the secular law must prevail.