The stalking statute, A.R.S. section 13-2923, states in pertinent part:
A. a person commits stalking if the person intentionally or knowingly engages in a course of conduct that is directed toward another person and if that conduct either:
Would cause a reasonable person to fear for the person's safety or the safety of that person's immediate family member and that person in fact fears for their safety or the safety of that person's immediate family member.
Would cause a reasonable person to fear physical injury to or death of that person or that person's immediate family member and that person in fact fears physical injury to or death of that person or that person's immediate family member.
B. Stalking under subsection A, paragraph 1 of this section is a class 5 felony. Stalking under subsection A, paragraph 2 is a class 3 felony.
C. for the purposes of this section:
1. "Course of conduct" means maintaining visual or physical proximity to a specific person or directing verbal, written or other threats, whether express or implied, to a specific person on two or more occasions over a period of time, however short, but does not include constitutionally protected activity.
A statute is unconstitutionally vague if it does not provide persons of ordinary intelligence reasonable notice of prohibited behavior and if it "fails to provide explicit standards for those who apply it," allowing for arbitrary and discriminatory enforcement. State v. Tocco, 156 Ariz. 116, 118, 750 P.2d 874, 876 (1988) (citing Grayned v. City of Rockford, 408 U.S. 104, 108-09, 33 L. Ed. 2d 222, 92 S. Ct. 2294 (1972)).
A defendant has standing to challenge a statute as vague only if that defendant has suffered a threatened or actual injury because of the alleged vagueness. State v. Lefevre, 193 Ariz. 385, 389, 972 P.2d 1021, 1025 P16 (App. 1998).
However, with the exception of challenges based on First Amendment grounds, a defendant whose conduct clearly falls within the legitimate purview of the statute has no standing to challenge the statute as vague. See State v. Steiger, 162 Ariz. 138, 144-45, 781 P.2d 616, 622-23 (App. 1989).