If a plaintiff sues two defendants for a car crash, can one defendant bring up an unrelated claim against the other once a related counterclaim is established?

The reasoning behind the correctness of the chosen answer lies in the rules governing the joinder of claims in federal court, particularly under Rule 18 of the Federal Rules of Civil Procedure. Rule 18 allows a party to assert multiple claims, whether they are related or unrelated, against an opposing party in the same action. This means that once a related counterclaim has been established, the defendant is permitted to introduce unrelated claims against the other defendant.

This ability to introduce unrelated claims forms part of the broader purpose of promoting judicial efficiency and avoiding piecemeal litigation. The rule encourages a comprehensive resolution of all claims and counterclaims arising from the same factual situation or transaction, but it does not restrict a party from adding unrelated claims as long as they are filed under the appropriate procedural guidelines.

By allowing the introduction of unrelated claims under Rule 18, the legal system facilitates a more streamlined and effective adjudication process. It minimizes the need for multiple lawsuits regarding different claims that can be resolved in the same venue. Hence, the reasoning behind the correct answer acknowledges the broad latitude provided to defendants in asserting claims within ongoing litigation.