What is the burden of establishing that a defendant has a right of petition or free speech in furtherance of their First Amendment rights in connection with a public issue?

Although the statute clearly places the burden on the plaintiff or cross-complainant to establish a probability of prevailing on the claim ( 425.16, subd. (b)), this burden does not arise unless the claim is one falling within the ambit of the statute. The statute is silent as to whether the defendant, as the moving party, has the burden of establishing the action arises out of acts in furtherance of defendant's First Amendment rights in connection with a public issue or whether the plaintiff bears the burden of showing its claim does not arise out of such acts by the defendant. A related question is what the statute means by the "furtherance" of the defendant's "right of petition or free speech." If the defendant's act is not constitutionally protected how can doing that act be "in furtherance" of the defendant's constitutional rights? On the other hand, if the defendant's act is constitutionally protected then, by definition, there is no probability the plaintiff will prevail on its claim. (Protect Our Mountain v. District Court, supra, 677 P.2d at pp. 1368-1369)