Some kind of pullback had to be expected after Monday's massive rally that breathed life back into the moribund equity market. But the action Wednesday has been below the standards of what traders expected, and economic data are largely to blame.

"Today is a little disappointing because I thought we would have treaded water, or sold off slightly, but this is a pretty significant selloff," says Paul Brigandi, vice president of trading at Direxion Funds.

The...