UPDATE, 2 PM: The market deteriorated as the day wore on, continuing the worst market slump since 2008. The Dow Jones U.S. Broadcasting and Entertainment Index closed down 7.3% — exceeding the 5.6% decline in the Dow Jones Industrial Average, 6.7% drop in the Standard & Poor’s 500, and 6.9% fall at NASDAQ.  CBS’ -10.3% slide made it the leading loser among media’s Big Guns. It was followed by News Corp (-7.7%), Viacom (-7.1%), Comcast (-6.6%), Sony (-6.4%), Disney (-6.1%), and Time Warner (-5.8%).

Double-digit losers include AMC Networks (-12.8%), LIN TV (-12.7%), Sirius XM (-12.7%), RealD (-12.6%), Cumulus Media (-11.9%), TiVo (-11.4%), Entercom (-10.9%), Westwood One (-10.8%), and E.W. Scripps (-10.3%). Those losing at least 9% include National CineMedia, Dish Network, Arbitron, Sinclair Broadcasting, Rovi, Outdoor Channel, Crown Media, Electronic Arts, Cablevision, and Coinstar.

PREVIOUS, 11:22 AM: It’s another terrible day for media and entertainment stocks as markets reel from Standard & Poor’s downgrade on Friday of U.S. debt — followed today by its downgrade of mortgage finance agencies Fannie Mae and Freddie Mac. The Dow Jones Industrial Average is down 3.7% at mid-day while the S&P 500 and NASDAQ are -5%. Among the Big Media companies, CBS (-8.8%) was hardest hit, followed by Sony (-4.8%), Time Warner (-4.8%), News Corp (-4.8%), Comcast (-4.5%), Disney (-4.3%), and Viacom (-4.3%).

No company on our watch list is up. Among all major media, Barnes & Noble, AMC Networks, and Sinclair Broadcasting are down more than 10% and Entercom is down more than 9%. Cumulus Media, McClatchy, and Westwood One are off at least 8%. Sirius XM, Rovi, Liberty, Pandora Media, TiVo, Coinstar, Cablevision, LIN TV, DreamWorks Animation, and McGraw-Hill (which owns Standard & Poor’s) are down at least 7%.