If π from Ohio has a related claim against ∆ after ∆ brings their counterclaim, what happens?

The correct answer reflects the principles of compulsory counterclaims as outlined in the Federal Rules of Civil Procedure. In this scenario, when the defendant (∆) brings a counterclaim against the plaintiff (π), if the plaintiff has a related claim against the defendant, that claim is categorized as a compulsory counterclaim.

A compulsory counterclaim is defined as any claim that arises out of the same transaction or occurrence that is the subject matter of the opposing party's claim. This means that if the plaintiff's claim is related to the defendant's counterclaim, the plaintiff must assert that related claim in the current action or risk losing the ability to bring it later. The rule encourages the efficient resolution of all claims that are interrelated and helps to prevent multiple lawsuits over the same set of facts.

Other options provided do not align with this principle. While a plaintiff could technically choose to waive a claim (first option), this is not applicable if the claim is compulsory. The suggestion that the claim can only be pursued in state court (third option) ignores the conditions under which claims may be litigated federally under supplemental jurisdiction. Finally, the option regarding filing an unrelated claim (fourth option) does not apply when the focus is on a related claim, which must be addressed