A claim by a defendant opposing the claim of the plaintiff and seeking some relief from the plaintiff for the defendant.
A counterclaim contains assertions that the defendant could have made by starting a lawsuit if the plaintiff had not already begun the action. It is governed by many of the same rules that regulate the claims made by a plaintiff except that it is a part of the answer that the defendant produces in response to the plaintiff's complaint. In general a counterclaim must contain facts sufficient to support the granting of relief to the defendant if the facts are proved to be true. These facts may refer to the same event that gave rise to the plaintiff's cause of action or they may refer to an entirely different claim that the defendant has against the plaintiff. Where there is more than one party on a side, a counterclaim may be made by any defendant against any plaintiff or plaintiffs.
According to the rules governing federal civil procedure, a defendant usually is required to make a counterclaim in an answer if the counterclaim arises from the same transaction or occurrence on which the plaintiff is suing. This is called a compulsory counterclaim because the claim must be made in response to the plaintiff's complaint and cannot be made later or in a separate lawsuit. There are also permissive counterclaims that may be made in the defendant's answer at a later time. A claim against the plaintiff that is based on an entirely different event is one kind of permissive counterclaim. For example, a man may sue a woman for money damages because of a minor injury and some property damage after their cars collided. Under the rules governing pleading in most courts, the woman would be required to assert a demand for money damages for the same accident in her answer to the man's complaint or she would lose the right to sue on that claim. If the man also happens to be a neighbor who borrowed the woman's chain saw and never returned it, the woman could demand return of the saw as a counterclaim or she could wait and sue the man for that at some other time. She might decide to wait in order to sue in a different court or because she does not want to argue the different circumstances of both claims before the same jury.
A defendant usually cannot make a counter-claim if it is not possible to make the same claim by starting a lawsuit. For example, a lawsuit to collect on a claim cannot be started after the period of time allowed by a statute of limitations has run out. In certain situations, however, a defendant may assert an expired cause of action as a counterclaim. This procedure, allowed for reasons of fairness and justice, is called equitable recoupment. The court may reduce the plaintiff's money damages up to the amount of the defendant's counterclaim, but the defendant will not be allowed an affirmative recovery of money over and above the amount to which the plaintiff may be entitled.