States have the right to defend its citizens. While there are exceptions. One state can punish the citizens of another state, if that person has committed something wrong or violated the domestic law of that state, and the state of which the person is a nationality, can not bring up a law suit against the other state. This is the famous principle called "clean hands" principle. While, it is the territorial jurisdiction of a state to punish any crimes happen inside its territory, the state shall always punish crimes in a proper way, within the proportionality principle.
Question:
Give some examples of "clean hands" principle. And have any state ever declared its right to protect citizens because the other state punishes his citizens beyond the proportionality?

