After a great start to the day, stocks have fallen hard in afternoon trading, with the the Dow Jones Industrial Average (DJINDICES:^DJI)down 10 points as of 2:30 p.m. EDT after rising triple digits in the morning. Nike's (NYSE:NKE) not helping the matter, as investors have crushed the athletics giant's stock today in the wake of its earnings report yesterday. Meanwhile, Symantec (NASDAQ:NLOK) has been blasted after a shocker that shook up Wall Street today. Let's catch up on what you need to know.

Nike's future fears
Nike's shares have plunged by 4.1% today, far and away the worst performer of the Dow so far. The company's most recent quarter actually pulled off a respectable performance for investors: revenue jumped 12% to $6.97 billion, topping analyst expectations and pushing earnings to $0.76 per share, a mark that also managed to beat Wall Street's projections. However, today's big drop isn't about what's in Nike's past, but what the company sees in its future.

Investors bailed on the stock after the company projected sales growth only in the mid-single digits for this quarter, far below the 12% growth analysts expect out of the company. Blame the stronger dollar for currency woes that Nike expects to cut into international sales, a particular problem as the company makes up 45% of its total revenue from outside of the United States. The dollar's pushed against the euro lately, and with Nike's Western European sales picking up steam in recent quarters, its results could take a hit across the Atlantic.

Most concerning for investors comes from the other side of the Pacific, however. Nike cautioned that sales in China could fall flat or even decline for the quarter, raising new fears that it is missing out on growth in the world's most promising emerging market. Chinese sales did jump by 7% in the last quarter, but with athletics goods in high demand there, along with the ongoing climb in the country's middle class and urban populations, Nike's in no position to sacrifice footing in this lucrative market. Competition has hurt Nike in China in recent years, and investors have to keep a close eye on whether the company can continue to push forward overseas in coming quarters.

Perhaps today's biggest market shake-up comes from outside of the Dow, however. Symantec stock is off by a massive 12.7% after the software and computer security specialist unexpectedly sent CEO Steve Bennett packing. While Wall Street's been high on Bennett in the recent past, Symantec judged its leader to be too slow in pushing for innovative changes in a company, according to sources cited by The New York Times and The Wall Street Journal.

Symantec hasn't yet taken hold of the mobile computing niche for its security software and is dealing with sluggish growth and rising competition. Nonetheless, analysts had seen the company headed toward better days under Bennett, and the shocking firing leaves Symantec headed toward an uncertain future. Keep a close eye on how the company's search for a new CEO goes, as it will speak to what Symantec's looking for in its future.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.