Dow futures soared 5% Friday and triggered ‘limit up’ trading rules—here’s how that works

U.S. stocks have been experiencing some of the most volatile trade in a decade and that trend is continuing Friday morning, with the three main stock-index futures up against a 5% limit-up volatility rule, a day after the S&P 500 index and the Dow Jones Industrial Average marked their worst one-day decline since the 1987 crash.