It's been a while since the S&P 500 Index (SNPINDEX:^GSPC) has seen a day as bad as this one -- more than three months, as a matter of fact. Stumbling to its largest single-day losses of the year, the S&P fell more than 1.8%, or 27.8 points, to close at 1,487 Monday. Here's how bad today was: Only 16 of the 500 stocks in the index posted gains, and just four stocks advanced more than 1%. With that in mind, today's three biggest laggards seem particularly awful.

F5 Networks (NASDAQ:FFIV) a network technology company, lost more than any other stock in the index, dropping 7.1%. The stock was downgraded to a "sell" rating by one research firm, with its $70 target price implying a 25% drop, even from today's depressed levels. One reason for the decline was today's announced venture with Websense, which the research firm Off Wall Street doesn't think will work out in F5's favor. 

The second-largest decliner of the day was Chesapeake Energy (NYSE:CHK), which cratered 6.8% as the business announced it would sell some of its highly desired land assets in Oklahoma on the cheap to China Petroleum & Chemical. Chesapeake shareholders hate to see fire sales like today's, where acres went for $2,400 apiece, far less than the $3,400 per acre some analysts expected. 

The last of the day's underperformers was life insurance company Genworth Financial (NYSE:GNW), which fell 5.6%. Genworth is also dealing with woes related to selling parts of its business. The stock tanked after announcing that the company had appointed current CFO Martin Klein to oversee certain "divestitures" that are seen as too peripheral to Genworth's main business.