Usually, I see 30k - 50k ES futures contracts traded in HFT style, when certain support / resistance levels MUST be breached. Same style applies to FDAX, FTSE, Hangseng, Nikkei, Kospi, Taiex, ASX, CAC 40, Eurostoxx...etc.
Usually, I play this song when such events occur :
The Doors: Break...