We examine the impact of COVID-19 on market structure in the U.S. Specifically, we analyze the impact of both the COVID-19-induced market uncertainty period as well as the suspension of the NYSE floor on trading dynamics such as market fragmentation, algorithmic trading, and hidden liquidity in the market. During both the heightened market uncertainty and NYSE floor suspension periods, we find a significant increase in hidden liquidity yet significant decreases in both algorithmic trading and market fragmentation. However, despite withdrawing from the market during this period, remaining algorithmic traders appear to improve market quality. Our results indicate that COVID-19 had a significant impact on order routing, pre-trade transparency, and automated trading.

We examine the information content of off-exchange retail order flow relative to off-exchange institutional and on-exchange order flow. We use alternative sources of retail order identification and account for the fact that market opacity affects the order routing choices of both institutions and the brokers who sell retail orders. After controlling for volume effects, we find that retail order flow is more informed than off-exchange institutional order flow. Off-exchange price discovery comes mostly from retail order flow. However, on days with greater Robinhood activity, the information content of retail order flow drops. Our results reconcile some mixed findings in this literature.