Nike is finally getting scuffed up. One of the longstanding darlings of Wall Street — praised for its advertising clout and product innovation — has had a rough year. The shares are down 13 percent in 2016 as analysts and investors fret over market-share losses to Adidas and Under Armour in the U.S., its largest region. Chief Executive Officer Mark Parker will get a chance to rebut critics on Tuesday, when Nike reports results for the quarter through August, traditionally its largest revenue-generating period.