NV Rev Stat § 171.137 (2020)
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2. If the peace officer has probable cause to believe that a battery described in subsection 1 was a mutual battery, the peace officer shall attempt to determine which person was the primary physical aggressor. If the peace officer determines that one of the persons who allegedly committed a battery was the primary physical aggressor involved in the incident, the peace officer is not required to arrest any other person believed to have committed a battery during the incident. In determining whether a person is a primary physical aggressor for the purposes of this subsection, the peace officer shall consider:
(a) Prior domestic violence involving either person;
(b) The relative severity of the injuries inflicted upon the persons involved;
(c) The potential for future injury;
(d) Whether one of the alleged batteries was committed in self-defense; and
(e) Any other factor that may help the peace officer decide which person was the primary physical aggressor.