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From a technical standpoint, Grasso also noted that since June 2013, every time the S&P 500 broke below the 100-day moving average, the market only stayed below that line "for a maximum of about four days."
The critical point, he added, was 1,958 in the S&P. That could signal that stocks were "grinding lower to that 200-day, which we haven't tested in two years."
RiskReversal.com's Dan Nathan saw a sign in Disney stock, which at one point had sold off $3.
"That's real selling in one of the biggest stocks on the planet," he said.
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Nathan said that weakness in the large-cap name suggests "there is going to be legs to the selloff."
"Some damage was done … and I think there's more to come," he added.
Triogem Asset Management's Tim Seymour said the U.S. economy was "definitely strengthening," citing jobless claims at an eight-year low.
"We're back at 2006 levels, people," he said. "The job market looks very health relative to itself, relative to at least the last five or six years."
The level to watch in the S&P 500 is 1,940, Seymour added.
"That's a place where a lot of traders were looking," he said. "It's a place where technically if it broke that and didn't climb back above today, I think we'd be telling a different tale tonight."
The S&P 500 closed up 0.01 percent at 1,946.17.