Mass shootings are incidents in which several people are injured or killed due to firearm-related violence, specifically for the purposes of this article, a total of four or more victims.
[6][7] The crowdsourced Mass Shooting Tracker project applies the most expansive definition: four or more shot in any incident, including the perpetrator.
"[10] The authors of the study further suggested that "the definition of mass shooting should be four or more people, excluding the shooter, who are shot in a single event regardless of the motive, setting or number of deaths.
All definitions can be exceeded with a single shotgun blast into a target cluster at short range.
The classification of a bystander struck by police while attempting to take out a believed perpetrator falls into a gray zone.