A counterclaim is a claim the defendant brings against the plaintiff in the same lawsuit — effectively suing back within the existing case rather than filing a separate action.
Compulsory vs. permissive counterclaims
A compulsory counterclaim arises from the same transaction or occurrence as the plaintiff's claim and generally must be raised now or it's lost. A permissive counterclaim is unrelated and can be brought here or in a separate case.
Plead it like its own complaint
A counterclaim needs the same elements as any complaint — specific facts supporting each element of the claim, not just a general assertion that the plaintiff also did something wrong.
It's filed within the answer, on a deadline
Counterclaims are typically included with the answer to the original complaint, on the same response deadline — missing that deadline can mean losing a compulsory counterclaim entirely.
Consider the leverage it creates
Beyond the claim's own merits, a well-supported counterclaim often shifts settlement dynamics — a plaintiff facing their own exposure has more incentive to resolve the whole dispute rather than push forward.