Market Maker Role in Volatility
The theoretical role of a market maker during volatility is to provide liquidity — to stand ready to buy when others are selling and sell when others are buying — thereby dampening price movements. In exchange for this role, market makers are permitted trading advantages not available to other participants.
The 2010 Flash Crash Lesson
During the May 6, 2010 Flash Crash, numerous HFT market makers withdrew liquidity, dramatically worsening the price decline. This event demonstrated that the market-maker liquidity commitment — typically informal for HFT firms — can evaporate precisely when it is most needed. Regulators responded with circuit breakers and Limit Up-Limit Down protections.
COVID-19 Volatility and Citadel's Revenue
During the March 2020 COVID-19 market volatility, Citadel Securities reportedly doubled its profit and generated approximately $4 billion in revenue in the first half of 2020. The firm benefited from increased trading volume and volatility. Whether this occurred because Citadel provided liquidity during the crisis or extracted profits from the volatility is a matter of characterization — both things can be simultaneously true.
Concentration and Systemic Risk
The concentration of retail market-making in a small number of firms raises systemic risk questions. If Citadel Securities experienced a major operational failure or withdrew from market-making during a crisis, the resulting liquidity vacuum could amplify market stress. This concentration risk is part of the regulatory case for treating Citadel Securities as systematically important.