Stocks chalked up big losses Thursday as the indexes punctured their 50-day moving average lines. The Nasdaq lost 1.9%, while the S&P 500 and the Dow Jones industrial average lopped off 1.6% and 1.5%, respectively. The small-cap Russell 2000 slid 1.6%. The IBD 50 slid 2.1%. Volume eased on the NYSE but rose on the Nasdaq, slapping the Nasdaq index with a distribution day.