Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos) By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
Second Section – the Negative Commandments
43. It is a negative commandment “Do not strike another Jewish person.”
As it states in Devarim (Deuteronomy) 25:3, “do not add more.”[this is talking of a case when a person deserves 40 lashes] This is a warning not to strike a Jewish person. From this, a person can learn using reasoning of “since this is true, how much more so true is something else”: if in a case where a person deserves lashes, which the Torah gave permission to strike, the person administering the lashes is told he is not allowed to hit the punishable one more times, how much more does it apply to striking other people.
If someone strikes his friend and injures him with an injury worth less than a prutah (about 1 cent), he receives whiplashes as a punishment. But, if he injures him with an injury more than a prutah (which means he causes damages worth a prutah or more), since he is required to pay money, he is not whipped (but he does transgress this negative commandment). Even if a person only raises his fists to hit someone, he is called a “wicked” person. A person that strikes another because of discipline or to teach a lesson does not transgress this commandment.