"I have a feeling futures will be up a little bit (Friday). Whether we hold is a different story," said Scott Redler, partner with T3Live.com.
There's some important data Friday including ISM Manufacturing, construction spending and consumer sentiment, all expected at 10 a.m. ET. There are also monthly vehicle sales, which could be strong, at an annualized selling pace of 17 million.
Earnings are expected from Chevron, CVS Health, Clorox, Duke Energy, Moody's, Public Service, TransCanada, VF Corp., Weyerhaeuser, Madison Square Garden, Aon and Calpine.
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The market's declines Thursday were led by the small-cap Russell 2000, down 2.2 percent and the Nasdaq, down 1.6 percent.
"It feels like for a lot of momentum names, there are some that are bent, and some are broken. As for the bios, at this point, they're oversold but this doesn't mean it's a bottom for the group," said Redler.
Traders have been watching the iShares Nasdaq Biotechnology ETF IBB this week, as a potential signal for momentum stocks overall and for the broader market. The IBB fell through its 50-day moving average and was hovering just above its 100-day. The Global X Social Media Index ETF SOCL was 2.3 percent lower Thursday, and it could fall further Friday after LinkedIn dropped about 20 percent in late trading after disappointing earnings. LinkedIn follows Twitter and Yelp, which also declined sharply on disappointing earnings news.
"There's definitely question marks about whether this selloff will be deeper than what we've seen so far in 2015. At this point, people are more defensive versus risk on. The question is will there be downside follow through," said Redler. "Two weeks from now, it feels like we'll be lower rather than higher. It feels like we need to see 2040/2050 on the S&P before we see new highs."
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Traders entered the week watching the S&P 500 to see if it would extend gains from record highs, but instead of breaking out, the index came off its highs Monday in an outside day, signaling more declines.
Scott Wren, senior equity strategist at Wells Fargo Investment Institute, said he does not see the current rout as a precursor to "sell in May" behavior. That's the old Wall Street adage that the stock market is weak in May through October, and traders should sell in May and then go away until the fall. The market's performance is typically better in November through April.
"Biotechs, based on our work, were overdone to the upside. Clearly health care has been a good performer," Wren said. "Probably 80 percent of the performance of that group has been solely due to the biotechs … it's very stretched."