Rule 13.Counterclaim and crossclaim

A party who has a claim against an opposing party arising from the same transaction or occurrence as that party's own claim must raise it as a counterclaim, so long as doing so does not require adding someone the court cannot exercise jurisdiction over. That obligation has narrow exceptions — if the claim was already the subject of another pending case, or if the opposing party sued only through attachment or similar process that never established personal jurisdiction. Anything that does not have to be raised can still be brought voluntarily as a permissive counterclaim.

A counterclaim does not have to match or offset the opposing claim; it can seek more, or something entirely different in kind. The rule does not, however, expand any existing right to counterclaim against the state or a political subdivision. A counterclaim that matures after the pleadings close can come in through a supplemental pleading, and one left out by oversight or excusable neglect can be added later by amendment with the court's permission. Rule 13 also covers crossclaims — claims one party brings against a coparty arising from the same transaction, occurrence, or property — and ties additional parties and separate trials back to Rules 19, 20, 42, and 54.