Subsection 2 of NRS 171.137 reinforces the idea that arrest is mandatory on a domestic violence call. This subsection deals with “mutual battery.” Mutual battery is when both domestic partners hit each other. Typically this occurs after the parties have been drinking, get into an argument, and the argument escalates into something physical. The girlfriend slaps the boyfriend, the boyfriend pushes her back. Mutual battery has occurred. NRS 171.137(2) says that in the case of “mutual battery,” the police officer has to determine who the “primary physical aggressor” is and arrest that person. According to the statute, the officer “is not required to arrest” the person who isn’t the primary aggressor.

The “primary physical aggressor” is not necessarily the person who hits first, but the person who causes the greater injury. So if a girlfriend throws a drink on her boyfriend and he punches her in the face, the boyfriend is the “primary physical aggressor” even though technically she committed a battery first. Beyond relative physical injury, in determining who the “primary physical aggressor” is, police consider prior domestic violence arrests, and any other factor they might think is relevant.

Technically, there is an exception to this rule built into NRS 171.137(1). The statute says a police officer can decide not to arrest anyone if “mitigating circumstances exist.” This means that if a police officer believes it would not be in the interests of justice to arrest a person, the law does not require him to do so. In theory, this sounds like a major exception, especially since the statute is titled “Arrest required for suspected battery constituting domestic violence.”

In practice, however, this exception is all but nonexistent. Las Vegas Metropolitan Police Department officers rarely, if ever, seem to think “mitigating circumstances exist”—even when the alleged “battery” is extremely minor, the alleged batterer has no criminal record, and the alleged victim doesn’t want the arrest to happen. In fact, I am not sure that many Metro officers even know the exception exists, given how many of my clients have been told by responding officers that the law required them to make an arrest on a domestic violence call, no exceptions.