Good guy with a gun

A good guy with a gun, in American gun control debate, refers to the idea that the best way to prevent a mass shooting is with high accessibility of weapons to civilians and police willing to stop an attack. The phrase originates with Wayne LaPierre in 2012, who stated that "the only way to stop a bad guy with a gun is with a good guy with a gun."

History and usage
On December 14, 2012, Wayne LaPierre, one week after the Sandy Hook Elementary School shooting, in a press conference announcing the NRA's National School Shield Emergency Response Program, stated that "the only way to stop a bad guy with a gun is with a good guy with a gun." This is considered to be the first mainstream usage of the phrase.

At the 2022 NRA Convention, soon after the Robb Elementary School shooting, Ted Cruz stated a variation of the phrase, saying that "what stops armed bad guys is armed good guys."

Analysis
It is unclear whether the presence of a good guy with a gun prevents mass shootings.

A 2013 study by Texas State University criminologists analysed 160 active shooter incidents finding only one in three to been prevented by lethal force from police or civilians. None of the incidents involving school shootings in the study were ended by armed guards or armed staff. Instead, the shooter was often restrained by unarmed staff. However, a plurality of active shooter incidents are resolved by the attacker fleeing or committing suicide. The presence of armed guards does little to deter school shooters, with Santa Fe High School, Stoneman Douglas High School, Great Mills High School, and Marshall County High School being prominent examples of school shootings against schools with armed guards. A 2020 study found "no association between having an armed officer and deterrence of violence" and that an "armed officer on the scene was the number one factor associated with increased casualties."