R. Yitzchak says: Even a man who intends to smite one and smites another is not liable—until he makes it clear that it is this man that he wishes to smite, as it is written (Devarim 19:11) "and he rise up against him and he smite him, etc." What, then, is the intent of "and if men fight, etc."? From (Leviticus 24:17) "And if a man smite any soul of man" I would understand even an eight-month birth, (who is destined to die); it is, therefore, written ("and if men fight," to indicate that) he is not liable unless he kills one who is (otherwise) destined to live.