Responsa for Bava Kamma 65:12

Q. B swore to leave all his disputes with A, to C and D for arbitration. Subsequently, B vilified A's father calling him shameful names, to which A retorted: "not my father, but your father". B became enraged at the insult to his father who had been a scholar and a sage. Both fathers were dead at the time. Now B demands that A be duly punished for vilifying a scholar after his death.
A. We have no right to adjudicate fines, but a court is permitted to take emergency measures whenever necessary. However, if A will take an oath to the effect that he did not fully understand the charge B had made against his father but automatically replied, "your father", he will be free from obligation. Moreover, B must leave this dispute also to C and D for arbitration. He can not press this charge separately without transgressing his oath. On the other hand, since people customarily and automatically reply "your father" whenever someone vilifies their father, B deserves greater punishment than A since he was the first to use vile language. In any event, both A and B should appear before a scholar seeking atonement for their sin of having vilified the dead.
SOURCES: Cr. 298.

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.