An action by a defendant in an action, against the plaintiff in the same action, upon the same contract, or for the same tort; as, if Peter bring an action of trespass against Paul, and Paul bring another action of trespass against Peter, the subject of the dispute being an assault and battery, it is evident that Paul could not set off the assault committed upon him by Peter, in the action which Peter, had brought against him; therefore the cross action became necessary.