When an Anti-SLAPP defendant lodges a factual challenge, district courts may properly consider extrinsic evidence in evaluating whether a defendant has met her prima facie burden under either step of the Anti-SLAPP analysis. If a defendant moves to strike “on purely legal arguments,” courts must analyze the motion under Rules 8 and 12, but where a defendant asserts “a factual challenge,” courts must treat the motion to strike as “a motion for summary judgment,” triggering discovery. These rules for Anti-SLAPP motions to strike apply in federal court regardless of whether a plaintiff challenges the first or second step of the anti-SLAPP analysis. And courts are entitled to rely on extrinsic evidence whether the challenge is as to the first step, the second step, or both steps.