EXOD580 The Talmud clearly states that causing someone else bodily harm is forbidden, just as causing bodily harm to oneself, is forbidden. Bava Kama 91b. If harming another human being intentionally is forbidden, then all wrestling and certainly all boxing should be forbidden for a Jew. And yet we see that these sports are permitted in certain circumstances. How can this be? Maimonides helps to provide an answer to this question. Although he rules it is forbidden to harm one's own body and certainly someone else's body, the prohibition is only if it is done between two people so angry at each other that they come to blows. Maimonides, Hilchot Chovel U'Mazik 5:1. The wording of Maimonides, "Derech Nitzayon" -- "In a manner of arguing," is based on the Torah word in the verse describing two people arguing that and then coming to blows (and accidentally striking a pregnant woman). (This verse with Rashi commentary). Therefore, only if people were arguing with each other and intending to cause bodily harm out of anger would a person be forbidden from striking another person. But a blow to the body in the course of a sporting match apparently would be permitted.