A crossclaim is a claim asserted between codefendants or coplaintiffs in a case and that relates to the subject of the original claim or counterclaim according to Black's Law Dictionary. A cross claim is filed against someone who is a co-defendant or co-plaintiff to the party who originates the crossclaim. In common law, a crossclaim is a demand made in a pleading that is filed against a party which is on the "same side" of the lawsuit.