contagious shooting
n.— «It is known in police parlance as “contagious shooting”—gunfire that spreads among officers who believe that they, or their colleagues, are facing a threat. It spreads like germs, like laughter, or fear. An officer fires, so his colleagues do, too.» —“50 Shots Fired, and the Experts Offer a Theory” by Michael Wilson New York Times Nov. 27, 2006. (source: Double-Tongued Dictionary)