NEW YORK (MarketWatch) - U.S. stocks fell sharply Tuesday as worries about European debt and the U.S. economy intensified. The Dow Jones Industrial Average DJIA, +1.19% fell 275.26 points to 10,965.00. The Standard & Poor's 500 Index SPX, +0.82% shed 29.60 points to 1,144.37. The Nasdaq Composite Index COMP, +0.74% declined 56.61 points to 2,423.72. Following a sharp drop in stock-index futures ahead of Wall Street's start, the New York Stock Exchange and NYSE Amex Cash Markets invoked Rule 48 for the open, lifting a requirement calling for price indications that help determine the floor price at the start to smooth trade.