I have found prohibitions against raising your hand as if to hit a friend, and things on physical punishment of children and wives, rulings on self-defense, and the rules of war. But is there a clear prohibition against non-lethal battery of strangers in peacetime? I’m interested in both the biblical and rabbinic sources on this. (Don’t worry, I have no plans to get into a bar fight.)
Shalom, Thank you for your question. There are several sources that forbid all types of (unwarranted) violence [- justified violence such as in times of war, self defense, certain educational settings, and by the police etc is permitted]. Firstly, as you mentioned, one who even lifts their hands to strike someone is called an evil person – all the more so if they actually strike them (see Talmud Sanhedrin 58b). Next, the Torah places a curse on someone who "strikes their fellow in private" (Devarim 27,24). Some commentators understand this verse to be talking about physical violence, which is cursed when carried out in such a way as to be un-punishable by the regular court system because it was carried out "in private". Additionally, the Torah commands the courts to enforce a punishment of lashes for certain crimes (Devarim 25,3). Because the Torah mentions explicitly the number of lashes and forbids going beyond that number. From this it is learnt that giving more than that number is itself a crime – and Rashi quotes the teaching that the words in the Torah "and do not add [to this number of lashes]" is the source to forbid striking someone. That is, if it is forbidden for the court to add even one lash too many, so too every person is forbidden from striking their fellow, as it is certain "adding" to what the Torah allowed. The Rambam (Laws of injury and damages 5,1) as well as the Shulchan Aruch, (Choshen Mishpat 420,1) quote this as definitive law. Here is the language of the Rambam – "It is forbidden for a person to injure anyone, neither his own self nor another person. Not only a person who causes an injury, but anyone who strikes in strife an upright Jewish person, whether a minor or an adult, whether a man or a woman, violates a negative commandment, as Deuteronomy 25:3 states: "Do not continue... to flog him." One may conclude that if the Torah adjures us against adding to the blows due a sinner, surely this prohibition applies with regard to striking a righteous person." Not only is this forbidden, but there are serious punishments and fines imposed on someone who did in fact break the law and hit someone. I hope these sources will be a good start for your continued study – stay safe! Blessings.