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.
Chasam Sofer(Gittin 7a): Mar Ukva said that there are people who are irritating me [verbal – Rashi]. … Even though it was only verbal abuse, nevertheless if it wasn’t for the fact that Mar Ukva could save himself from this abuse by arising early and going to the study hall - it would seem that he would have been allowed to report his abusers to the government… We see from Rashi’s explanation that it was clear that if Mar Ukva had been abused monetarily or by forgery he would have been permitted to report his abusers to the government and he would not have been required to go to the study hall. That is simply because if a person comes to kill you than you have every right to kill them first. This is also the ruling of the Rambam (Hilchos Chovel u’Mazik 9:11): “And similarly if a person abuses and harasses the community it is permitted to give him over to the secular government to be beaten… In contrast if only an individual is being harassed it is prohibited to report him…” This would indicate that the Rambam is referring to verbal harassment. Therefore if the assailant caused an actual loss it would be permitted to report him to the government so that he doesn’t cause further loss. This is the ruling of the Rema (C.M. 388:9) and it is also the ruling of the Shach (C.M. 388:59-60). However while it seems obvious to the Rambam that if one verbal harasses a community it is permitted to report him to the government – the commentaries don’t show the sources of this ruling. It must be that this ruling is learned from this gemora. It would seem that if hadn’t been for the fact that Mar Ukva had a solution to the harassment problem by going to the study hall it would have been permitted to report his assailants to the secular government. However this solution is only relevant for an individual. But it is not relevant for the community and therefore it is clearly permitted to report the community nuisance to the government. Also see the Pnei Yehoshua’s discussion of this gemora where he says that the solution of going to the study hall and complaining to G‑d about the assailant is not correct if one can stop the harasser in other ways. However he says if the harassers cause him to waste time from Torah and prayer because of his upset he can stop the harassers in any manner…
Shulchan Aruch(C.M. 425:2): Therefore for a pregnant woman whose life is in danger from difficult labor - it is permitted to cut up the embryo either by means of chemical or by hand. That is because the baby is like a pursuer (rodef) trying to kill her. However if the head of the baby is born it cannot be harmed. That is because we don’t sacrifice one life for another. Two lives in competition is simply the normal situation of the world.