AbstractResearch Question/IssueThis study examines whether social capital's monitoring role intensifies during post‐terrorism periods, as terrorism influences citizens' willingness to change society and increases stakeholder participation. Focusing on firms' stock price crash risk, caused by managers' opportunistic behavior (viz., bad news hoarding), we hypothesize that social capital under terrorism reduces stock price crash risk, as it is expected to play an external monitoring governance role.Research Findings/InsightsUsing US public firms, a county‐level social capital index, and terrorist attacks from 1992 to 2014, we find that social capital surrounding corporate headquarters significantly reduces stock price crash risk during post‐terrorism periods. The results are robust to propensity score matching and instrumental variable regressions, and a battery of sensitivity tests. Overall, we suggest that stakeholders' willingness (that is intensified by terrorism) to monitor firms' bad news hoarding is channeled through social capital. Furthermore, the monitoring role of social capital under terrorism is significant for firms with poor internal monitoring, more institutional investors, less entrenched managers, CEOs preferring bad news hoarding, and accompanied by improvement of analysts' forecasts, suggesting that the impact of external governance may differ by firms' governance characteristics.Theoretical/Academic ImplicationsWe contribute to the corporate governance literature by investigating the role of social capital as external governance. While terrorism brings serious damage and economic costs, our study shows that it gives rise to the increased role of social capital, suggesting a novel perspective that terrorism's unexpected socio‐psychological outcome, being non‐financial social threats, leads to positive corporate behaviors by stimulating stakeholders' willingness to monitor firms. Our study is also consistent with the literature that social capital particularly matters in certain periods, such as traumatic events. Furthermore, the impact of a firm's external monitor differs by its governance characteristics, highlighting the importance of corporate governance.Practitioner/Policy ImplicationsWe suggest that social capital serves as firms' external monitor by restraining managers' bad news hoarding under certain circumstances, providing implications for policymakers and practitioners. According to our results, traumatic events, such as terrorism, could be viewed as the moderator for the impact of social capital on corporates, emphasizing the need for intensifying social capital (or making it more effective) without tragic incidents. Meanwhile, one might view social capital as the mediator for the increased willingness of individuals to monitor during the post‐terrorism period, highlighting the need for sufficient social capital in the local community.