This mitzvah is the command concerning the laws of one who injures his fellow, from "And if men quarrel and one strikes his fellow" (Shemos 21:18). These are the dinei kenasos: the injurer pays from his money for the damage, even for humiliation, and only ordained judges in Eretz Yisrael may rule on them.
https://www.torahrecordings.com/rambam_sefer_hamitzvos/001/236