On a rainy evening in Moscow during the World Athletic Championships, the world’s premier sprinter, Usain Bolt, reclaimed his world title, running a 9.7 100-meter dash, beating Justin Gatlin and fellow Jamaican teammate Nesta Carter, who finished third. It was not a good meet for a number of world-class sprinters, including Asafa Powell, Sherone Simpson and Jamaica’s world-record holder, Veronica Campbell-Brown. They all tested positive for using a banned substance.