Rule 14.Third-party practice.

A defending party may serve a summons and third-party complaint on someone outside the case who is or may be liable for all or part of the claim against it, though court permission is required if more than 10 days have passed since the original answer was served. The person brought in this way — the third-party defendant — must defend against that claim the same way any defendant would, must assert any compulsory counterclaim against the third-party plaintiff and may assert a permissive one, and may raise against the original plaintiff any defense the third-party plaintiff has, plus any claim arising from the same transaction as the plaintiff's claim.

The plaintiff, in turn, may assert against the third-party defendant any claim arising from that same transaction, and the third-party defendant must then defend against it and assert compulsory counterclaims the same way. Any party may move to strike the third-party claim, sever it, or have it tried separately, and a third-party defendant facing its own exposure may bring in a further nonparty under this same process.

A plaintiff can use this same mechanism in reverse — bringing in a third party under the same conditions that would let a defendant do so — when a claim is asserted against that plaintiff.