Today's market weakness: the fact that we are beginning what is traditionally the weakest month of the year made traders jittery right at the outset; three separate events after stocks opened moved stocks down.
1) At 10 AM generally good economic news came out as pending home sales and ISM manufacturing index came in stronger than expected, while construction spending was a tad weaker, though the weakness was in non-residential.
Homebuilding stocks, which had been moving sideways for several days after hitting highs for the year, rallied for a minute or two, then sold off sharply.
Selling off on generally good economic news added fuel to the debate that stocks were overbought.
2) The increase in selling caused volatility to spike up, which created a dollar rally (dollar is a safe haven). Stocks weakened further, particularly commodity stocks like Freeport McMoran, Alcoa, Dow Chemical, US Steel.