Responsa על בבא קמא 65:8

A. An opinion is prevalent among the people that a takkanah of the communities frees one from any responsibility, if, after suffering bodily injury at the hand of his neighbor, and while still in the heat of anger, he retaliates with force, or even turns informer against him. If such takkanah exists, in order to punish severely the person who began the disturbance, or if B's claim is true that A released him from obligation in this matter, B owes nothing to A. But the takkanah of the communities probably frees the assaulted person, who retaliates in the heat of anger, from the special fines which communities usually impose upon offenders against public policy, but does not free him from responsibility for the injuries he inflicted upon the assailant. The judges, therefore, must evaluate the five compensations (prescribed to the injured person by the Talmud) for biting B's finger. If B caused A a greater loss than the amount estimated, the former must pay the difference to the latter.
SOURCES: Pr. 994; Tesh. Maim. to Nezikin, 15b; Hayyim Or Zarua, Responsa 142. Cf. Weil, Responsa 28.