Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

On days like today, when declining stocks outnumbered gainers by more than a six-to-one ratio, just about everywhere you look you see red. Merely unpopular stocks with a lack of momentum can't hope to distinguish themselves as the biggest laggards on days like this -- there's too much competition. Appropriately then, we find that the three worst stocks in the S&P 500 Index (SNPINDEX:^GSPC) today each had company-specific news that drove shares to steep, steep losses. The S&P 500 Index itself was off 38 points today, or 2%, to end at 1,790. 

International Game Technology (NYSE:IGT), the Las Vegas-based casino game manufacturer, plummeted a whopping 14.8% on Friday, as four layers of negative news compounded on top of each other to produce today's wealth-erasing result. The catalysts, from broad to narrow, were: steep losses in the stock market in general; bearish sentiment surrounding the gaming industry after worries about Macau and China surfaced this week; International Game Technology's earnings miss Thursday afternoon; and the revelation that the founders of social media gaming platform Double Down will be leaving IGT. Double Down was acquired two years ago for $500 million, and growth has been slowing for the last two quarters. The departure of Double Down's co-founders could pose a competitive threat to IGT down the line. 

Shares of robotic surgery innovator Intuitive Surgical (NASDAQ:ISRG) fell 6.4% Friday, also slumping after subpar quarterly earnings were announced on Thursday afternoon. Revenue fell 5% from the same quarter a year before, as sales of its prized da Vinci system waned. Intuitive Surgical is dealing with more cautious adoption of its technology in the medical field as it faced litigation issues stemming from its robotic procedures in 2013. 

Finally, shares of the $83 billion biopharmaceutical company Bristol-Myers Squibb (NYSE:BMY) lost 5.6% Friday, even after fourth-quarter sales exceeded expectations. Investors ignored the revenue beat and, instead, focused on the progress of Bristol-Myers Squibb's cancer treatments, which seem to be advancing more slowly than investors would like. Specifically, the company released a new lung cancer trial for its drug nivolumab, which shareholders took as a sign that current trials with Yervoy aren't going as planned.