What is the ruling on striking a youth who assaulted his father, in kind?

Undoubtedly, the act of a young man striking an elder is abhorrent. Allah Almighty has permitted retaliation in kind against the aggressor, but has favored forgiveness and reconciliation. The execution of retribution (qisas) rests with the ruler or the Sharia judge, and the victim is not permitted to retaliate personally. For an offense like a blow or a slap that does not cause a wound or impair the function of a limb, there is no qisas according to the majority of jurists, due to the impossibility of exact equivalence; rather, there is discretionary punishment (ta'zir). If the questioner's father refuses to forgive, he must refer the matter to the judiciary.