S&P 500 futures have been headed lower for most of the morning since around 6 AM ET, but the selling really accelerated at 8:30 with the release of better-than-expected initial jobless claims data, which may suggest that the Federal Reserve will be ready to begin tapering back its quantitative easing program as soon as the central bank's September policy meeting.
(Treasuries and gold are also taking a beating.)
At 9:15, the Federal Reserve reported weaker-than-expected industrial production growth, which was flat in July.
Right now, the S&P 500 is trading down 1.3% from yesterday's close at 1663. The Dow Jones Industrial Average, meanwhile, is also down 1.3%, or 200 points, to around 15,140.
The S&P 500 has closed down in six of the last eight trading sessions.
Thinkorswim