A new mishnah! But first - the written form of the Torah's verses, as compared to the read/pronounced form. Now, when one throws a stone into a public gathering - that person would go to exile in the city of refuge (among other cases, and with exclusions). Plus, cases between father and son, teacher and student, etc., where there might well be a mitzvah for the perpetrator to have a mitzvah for the action, including deliberate hitting (as compared to throwing a stone). With the Gemara doing the heavy duty lifting to interpret the mishnah. Plus, a jump to shemitah - and a comparison to voluntary action. Also, another mishnah: A father's accidental of a son, and a son's accidental killing of a father - the killer goes to the city of refuge. This right seems reserved to a Jew who kills a Jew (unless it's a ger toshav who kills a ger toshav). Note that the father who strikes his son for is own education is in a different category, because that might be a mitzvah, in context.