As we noted overnight, at 22:08:32 ET, a large wave of sell orders hit many stock index futures contracts. Most notably, Nanex notes [2], over 6,000 March 2014 eMini contracts traded in 1 second. After closer inspection, it appears that trading began almost simultaneously in several contracts, with the March 2014 eMini (ES) starting just a few milliseconds before the others. It's unclear whether the trades in the other contracts were a reaction to the eMini or part of the same sell program... but the slowness of reversion in prices makes it clear that while the mainstream media would like to shrug it off as just another "fat finger," it was anything but.
Via Nanex, [2]
Comparing ES, NQ, TF and YM at 22:08:32 on December 15, 2013.
Closeup of the collapse - and the clear indication it was not a single fat-finger trade...
(each pixel is 25 milliseconds)
[3]
and here each pixel is 1 millisecond...