Can a defendant sue another defendant for a related claim if both are being sued by the plaintiff in federal court?

The correct answer is that a defendant can sue another defendant for a related claim if both are being sued by the plaintiff in federal court, particularly if the claims are transactionally related. This situation is governed by the concept of permissive counterclaims and crossclaims under the Federal Rules of Civil Procedure.

When multiple parties are involved in a lawsuit, the rules allow for claims that arise out of the same transaction or occurrence as the original action to be brought together. This promotes judicial efficiency and helps resolve all related disputes in a single legal action. Thus, if one defendant has a claim against another that stems from the same incident or set of facts as the plaintiff's claims, they can bring this claim as a crossclaim against the co-defendant. These related claims can enhance the court's ability to settle all issues at once and reduce the chances of inconsistent judgments arising from separate lawsuits.

In contrast, the other options would impose unnecessary limitations or misunderstandings about the procedural rights and obligations in a federal court setting.