A claim by a defendant opposing the claim of the plaintiff and seeking some relief from the plaintiff for the defendant.
Once a plaintiff sues a defendant in a civil action, the defendant has the right to assert a legal claim of her own against the plaintiff. This is known as a counterclaim. A counterclaim makes assertions that the defendant could have made in a lawsuit if the plaintiff had not already begun an action. A counterclaim is distinct from a mere defense, which seeks only to defeat the plaintiff's lawsuit, in that it seeks a form of relief. There are two types of counterclaims: compulsory counterclaims and permissive counterclaims. Both are governed in federal court by rule 13 of the Federal Rules of Civil Procedure. The rules in state courts are similar.
The compulsory counterclaim arises from the same transaction or occurrence that forms the basis of the plaintiff's suit. For example, a car accident between two drivers leads to a personal injury lawsuit, but the defendant asserts in a compulsory counterclaim that the plaintiff actually owes him damages for injuries. A compulsory counterclaim generally must be part of the initial answer to the plaintiff's action and cannot be made later in the suit or in a separate lawsuit.
By contrast, the permissive counterclaim arises from an event unrelated to the matter on which the plaintiff's suit is based. For example, John Smith breaks his leg while visiting the home of Jane Doe. Smith sues Doe, alleging that she negligently left her child's roller skate on her front porch. In a permissive counterclaim, Doe asserts that Smith owes her money. The court will rule separately on plaintiff Smith's and defendant Doe's respective claims; if both claims are permitted to proceed, Smith v. Doe will involve the two parties' respective allegations of Negligence and a bad debt.
Counterclaims are usually valid only if it is possible to make the same claim by starting a lawsuit. Thus, in the example of Smith and Doe, Doe can only make her permissive counterclaim if the Statute of Limitations on collection of the debt has not expired. Permissive counterclaims need not be made in the initial Pleading; they can be made at a later time or even in another lawsuit. This flexibility may help the defendant's legal strategy: she can wait and sue in a different court, in order to have another judge hear the case or to avoid arguing the merits of separate claims before the same jury.