Rule 13. Counterclaim and Crossclaim
(a) Compulsory Counterclaim.
(1) In General. A pleading must state as a counterclaim any claim that—at the time of its service—the pleader has against an opposing party if the claim:
(A) arises out of the transaction or occurrence that is the subject matter of the opposing party’s claim; and
(2) Exceptions. The pleader need not state the claim if:
(b) Permissive Counterclaim. A pleading may state as a counterclaim against an opposing party any claim that is not compulsory.
(c) Relief Sought in a Counterclaim. A counterclaim need not diminish or defeat the recovery sought by the opposing party. It may request relief that exceeds in amount or differs in kind from the relief sought by the opposing party.
(d) Counterclaim Against the United States. These rules do not expand the right to assert a counterclaim—or to claim a credit—against the United States or a United States officer or agency.
(e) Counterclaim Maturing or Acquired After Pleading. The court may permit a party to file a supplemental pleading asserting a counterclaim that matured or was acquired by the party after serving an earlier pleading.
(g) Crossclaim Against a Coparty. A pleading may state as a crossclaim any claim by one party against a coparty if the claim arises out of the transaction or occurrence that is the subject matter of the original action or of a counterclaim, or if the claim relates to any property that is the subject matter of the original action. The crossclaim may include a claim that the coparty is or may be liable to the crossclaimant for all or part of a claim asserted in the action against the crossclaimant.
(h) Joining Additional Parties. Rules 19 and 20 govern the addition of a person as a party to a counterclaim or crossclaim.