NEW DELHI: The S&P BSE Sensex plunged over 439 points on Thursday to slip below its crucial support level of 28,000, led by losses in HDFC, ICICI Bank RIL , and Tata Motors.The Nifty50 slipped below 8,600, weighed down by losses in realty, power, metals, banks, and auto stocks.The selling was broad-based as both S&P BSE Smallcap and Midcap indices slipped more than 1 per cent each.ETMarkets.com collated list of five factors which could be weighing on Dalal Street:The minutes of the September 20-21 meeting, at which the US central bank held rates steady, showed a greater probability of a rate hike in December. Most market experts across the globe were not anticipating a rate action from the central bank in 2016.Several voting Federal Reserve policymakers judged a rate hike would be warranted "relatively soon" if the US economy continued to strengthen, but doubts on inflation remained, according to the minutes of the Fed's September policy meeting released on Wednesday."A rate hike in December is possible. They (Fed) have been talking like this for a while. The news has been pretty good. We knew it would be a close call," James E Glassman, MD, JPMorgan Chase & Co., said in an interview with ETNow."The market is getting used to the idea of a possible next move in December and according to me, it is just not the end of it," he said.Asian stocks stumbled to three-week lows after China's September trade data showed a sharp decline in exports, raising fresh concerns about the health of the world's second-biggest economy.China's September exports fell 10 per cent from a year earlier, far worse than expected, while imports unexpectedly shrank 1.9 per cent after picking up in August, suggesting signs of stability in the world's second-largest economy may be short-lived, said a media report.That left the country with a trade surplus of $41.99 billion for the month, the General Administration of Customs said on Thursday.Most of the IT-related stocks were trading with negative bias ahead of results of bellwether Tata Consultancy Services (TCS), and Infosys TCS is likely to report 0.2 per cent quarter-on-quarter (QoQ) drop in September quarter net profit on Thursday, October 13, at Rs 6,302.20 crore, according to a poll conducted by ETNow.According to a consensus estimate of analysts polled by ET Now, the country's largest IT company is likely to deliver 1.47 per cent quarter-on-quarter growth in revenues at Rs 29,735.30 crores for September quarter, compared with Rs 29,305 crore reported in June quarter.Infosys is expected 2.8 per cent QoQ growth in the net profit to Rs 3,531 crore for the quarter ended September 31 compared with 3,436 crores reported in the year-ago period.Metal stocks have come under pressure reflecting weakness in global metal prices after exports at the world's biggest metals consumer China fell more than expected in the month of September. Mining stocks such as Hindalco Industries and Vedanta Ltd also fell more than 1.5 per cent each.China's September exports fell 10 percent from a year earlier, far worse than expected, while imports unexpectedly shrank 1.9 percent after picking up in August, said a Reuters report.The Nifty50 slipped below its crucial support level of 8,650 and a close below 8600 or even 8,650 could attract further profit taking which could take the index towards 8,550 levels, experts suggest.The bulls will be able to regain some control over the D-Street if Nifty50 is able to surpass 8,750 on closing basis in this week."The Nifty50 has to cross and hold above 8,750 zone to witness a bounce back move towards 8,800-8,820 zone while holding below 8,680 might attract the profit booking decline towards 8,600 then 8,558 levels," Chandan Taparia , Derivatives & Technical Analyst - Equity Research at Anand Rathi Financial Services told ETMarkets.com.