The S&P 500 just tumbled below its 200-day moving average--a key technical level

The S&P 500 index on Monday is flirting with closing below an important, long-term trend line as selling intensified early Monday. The S&P 500 index SPX, -2.39% was off 2.6% at 2,572, firmly trading beneath its 200-day moving average at 2,589.93, according to FactSet data. Technical analysts pay attention to moving averages to help gauge bullish and bearish momentum in an asset. The Dow Jones Industrial Average DJIA, -2.17% meanwhile, was down 486 points, or 2%, at 23,625, while the Nasdaq Composite Index COMP, -2.65% turned negative for the year, off 3% on the session at 6,853. The S&P 500 last closed below its 200-day MA in late June of 2016.