Stocks ended the week on a down note Friday, but the selling pressure never got intense. After two straight closes above its 50-day moving average, the S&P 500 lost 0.7% and ended below the line. The Nasdaq fell 0.6%. Small caps fared the best as the Russell 2000 gave up just 0.3%. The IBD 50 also held up well, down 0.3%, helped by Ambarella (AMBA), which jumped more than 6.5%.