Bloomberg reported that it was a mistakenly placed ES e-mini order. I begin to think that these things are done deliberately. Say, some firm takes a short position and then drops the price. A few tricks like that may make them millionaires. It gets my heart racing everytime, because I begin to think of a terrorist attack.
Also I saw a lot of funny trades happenning at like 991-994 when the market was at 1000-1003. I tried to place a buy order for 994 but was not getting a fill though.