To further clarify: 75,000 e-mini contracts is not an astronomical amount. Orders of this size are not uncommon. To really understand what happened one must a

To further clarify: 75,000 e-mini contracts is not an astronomical amount. Orders of this size are not uncommon. To really understand what happened one must answer the question: what are the market conditions we have created such that a normal sized order can cause such a dislocation? A lot of this has to do with the practices of the HFT 'liquidity providers.' This is a complex topic, but the flash crash demonstrated what a lot of people have been saying for years: volume != liquidity, the HFT shops generate volume, not liquidity and engage in some practices (quote-stuffing, sub-pennying etc) which serve to systemically destabilize the markets. (and overload the market infrastructure)