The Nasdaq composite, which includes many technology companies, fell 21.12 points, or 0.7 percent, to 3,203.86.
F5 Networks, a network equipment and service provider based in Seattle, plunged 19 percent, the most of any S&P stock, after slashing its profit and revenue forecast. The company said its contract bookings fell sharply, as did its business with the federal government. The stock lost $17.21, or 19 percent, to $73.21.
The Dow Jones Transportation Average, which includes airlines like United and Delta Airlines and shipping companies like UPS and FedEx, was down 3.5 percent for the week, its biggest weekly decline since September. The index is seen as a leading indicator of the broader market.