I'm not a lawyer and I don't know how a counterclaim would work in this case, but the way I understand anti-SLAPP statutes to work is that they let the defendant file a motion to dismiss. If the suit were in state court, then the state law would clearly apply and Krebs could try to have the suit dismissed. But it's in federal court, not a Virginia state court. Whether state anti-SLAPP statutes can be used in federal cases is not clear; there's a circuit split and the Fourth Circuit has not ruled on question: https://www.jdsupra.com/legalnews/second-circuit-slaps-down-...
State court claims can and regularly are brought in federal court because federal courts have authority to hear state law cases. It’s Civil Procedure 101. Counter-claims which arise from the same operative facts must be brought or else they’re generally waived.
Also, defamation is a creature of common law and therefore state law governs it; there is no Federal defamation law. Ubiquiti filed in federal court under diversity jurisdiction, and likely because they think they'll get a better outcome than they would in state court. But the court still has to adjudicate the substantive claims under VA state law. Procedurally, though, the Federal Rules of Civil Procedure apply in Federal court, not state procedural rules.
The cited article suggests that some Federal circuits treat anti-SLAPP statutes as procedural rather than substantive law, and so federal judges might decline to apply them in the cases brought to them.
My understanding of the linked article is that the question is whether the federal rules of civil procedure supersede the state anti-SLAPP statue, because, since it’s in federal court, the suit is governed by the FRCP even if it’s over state or common law claims.
