What would disallow a counterclaim from establishing federal jurisdiction?

The correct answer highlights that a counterclaim which involves only state laws does not independently establish federal jurisdiction. Federal jurisdiction typically arises in cases involving federal questions or complete diversity of citizenship between parties, which allows a case to be heard in federal court rather than state court.

In the context of a counterclaim, if it solely pertains to state law issues, then it would not invoke federal jurisdiction. While federal courts may engage with state law claims under certain circumstances, such as when they are part of a broader case already involving federal questions or diverse parties, a state law-only counterclaim would not qualify on its own for federal jurisdiction.

Thus, a counterclaim that centers entirely around state law does not meet the necessary criteria for federal jurisdiction, which must involve either a federal question or diversity situation. Therefore, this situation would not grant federal jurisdiction to the counterclaim.