The S&P's decline came as the Nasdaq Composite plunged to within reach of the level viewed as an official correction, falling nearly 10 percent as of April 15 from its March high as investors ditched such "momentum" stocks as Apple, Tesla Motors, Twitter and Facebook.
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"Technically it wasn't a correction by the numbers. It was somewhat localized and narrow in areas of the market, specifically biotech, Internet retail, IPO stocks and social media," said Jim Russell, senior equity strategist for US Bank Wealth management.
"We do think that's over. But that does not prevent individual companies that drastically missed first-quarter earnings and gave weak guidance from being punished," Russell added.
The decline in new technology was likely related to valuation, as many of the companies involved "got to levels that were speculative," said Hugh Johnson, chairman of Hugh Johnson Advisors.
Still, Johnson wonders if the early April pullback represents "the correction we should have had in 2013, and whether there may be something that is troubling beneath the surface."
"We did get down to levels that had technical significance; the S&P 500 did not quite get there, but it was close," said Luschini, noting the index didn't hit the 200-day moving average or the trend line in place for some time. "At the same time, it was hardly at oversold levels."
In looking at the performance of the U.S. stock market since the end of last year, several things leave Johnson troubled.
For one, utilities have performed the best among the S&P 500's 10 major sectors, up more than 11 percent.
"That's not good news, and usually happens when investors become defensive. Staples have also performed well, that's another example that investors are worried about something," said Johnson.
Further, large companies have outperformed small companies, an indication that investors are becoming "cautious, risk adverse or worried," Johnson said.
Stock market headwinds include the unresolved Russian-Ukrainian geopolitical conflict. "Should that spin out of control, that's a negative," Russell said.