Report 407

Using intraday data on individual stocks included in the S&P 500 index, we present evidence of herd formation over the duration and aftermath of the Flash Crash on May 6, 2010, while no evidence of herding is observed preceding the event. The findings establish a clear link between herding among market participants and flash events that can drive sudden price fluctuations and underscore the importance of monitoring herd activity, particularly in the case of automated markets.