The story today is the collapse of the momentum stocks as Joe Sixpack runs for his life. The 10-stock momentum portfolio I set up is down 3.3% as I write today and 6% (ok, 5.94%, I exaggerate) since it was created on 8/15. Meantime, the Dow is down 44 and the S&P is down 9 and change, 0.5% or less.
No doubt in my mind that those stocks have been heavily shorted by the pros at the same time as they have been pimped to retail and the pros have decided it is time to collect.
So they short more, and then when the retail traders are scared or getting margin calls (or both) they cover their shorts by buying the stock from the weak hands who just bought them at much higher prices.