If any burgess be appealed of a plea whereon wager of battle may issue by a villein or outdweller , let him defend himself by oath, that is to say by the 36 men, unless he is challenged in respect of a crime that the law requires him to defend by battle, in no case ought a burgess to fight against a villein if he have challenged him unless before the dispute he shall have quitted the burgage.
Source: wiktionary