Gittin(88b): Shemos (21:1): “These are the laws (mishpatim) which you should place before them.” That means that you should place cases for judgment only before Jews and not non‑Jews. Another understanding of this verse is that cases for judgment should only be placed before judges who have semicha and not laymen…
Shulchan Aruch(C.M. 26:2): If the non‑Jews are the controlling power and the litigant is powerful in his own right and therefore the person can not recover what is his by the authority of the Jewish court – he should first summon his opponent to the Jewish court. If his opponent refuses to go – he should obtain permission from the Jewish court and then use the non‑Jewish court to recover what is his from his opponent. Rema: The Jewish court has the right to go to the non‑Jewish court and to testify that one person owes the other money. All this is only if one of the litigants refuses to obey the Jewish court. Otherwise it is prohibited for a Jewish court to give authorization for Jews to have their dispute presented to a non‑Jewish court..
Shulchan Aruch(C.M. 388:9): It is prohibited to inform on a Jew – either concerning himself or his money - to non‑Jews who are in power by force. This is prohibited even if he is a wicked person and a sinner and even if he causes aggravation and trouble to the potential informer. Rema: But the prohibition is only if he aggravates him with words. However if the Jew informs on him then it is permitted to inform on the Jew who informed. Because he has the right to kill the one who informed on him because of the fear the informer will reciprocate and inform on him to the secular authorities (Rosh 17:1, Rashba #181) or if it is impossible to save himself another way. However if he can he should save himself another way. Thus it is like two people who inform on each other. Whoever causes the greatest loss is obligated to pay the difference. Whoever gives over a Jew into the hands of non‑Jews – whether physically or monetarily – he has no portion in the world to come.
Sema(C.M. 388:30): For the sake of the harassment of the individual it is prohibited to report it to the secular authorities. This that the abuser is not reported to the secular authorities is only when he is verbally abusive but if he causes financial loss and surely if he beats him or causes bodily suffering it is permitted to report him to the secular authorities as is stated in the Rema and the Darchei Moshe
In sum a person has every right to defend himself by the rules of combat that have been determined by the plaintiff.