Police depend on prevailing descriptive and injunctive norms to maintain civil order. Yet, conformity to social norms is predicated on citizens sharing the same social reality where such norms of civility guide and constrain behavior. The invisible influence of law enforcement expectations on preparedness for January 6 suggests the critical social norm violated by crowd members at the Capitol was the injunctive norm against attacking police officers. The goal of this article is to address two central questions: (a) Why did crowd members attack police officers on January 6 outside the Capitol building? and (b) Why did existing descriptive and injunctive norms of civil behavior fail to prevent these violent acts leading to the Capitol breach? Emergent norm theory (ENT; Turner & Killian, 1987) and the focus theory of normative conduct (Cialdini, 2012) were used to analyze and provide initial answers to these questions. A case study method was employed using information about the January 6 Capitol riot and insurrection published in public domain news sources. The available case facts support hypotheses from ENT that justification, symbolization, feasibility, and timeliness were important influences on collective behavior. The emergent norm (“Stop the Steal”) changed the expected descriptive norm radically when people observed fellow crowd members using physical force to cross police lines and attack officers at the Capitol. Moreover, this emergent norm suppressed the restraining impact of the proscriptive injunctive norm. Research and practical implications for the prediction and prevention of similar future events are discussed. (PsycInfo Database Record (c) 2022 APA, all rights reserved)