A major scandal is erupting in the multibillion-dollar industry of fantasy sports, the online and unregulated business in which players assemble their fantasy teams with real athletes. On Monday, the two major fantasy companies were forced to release statements defending their businesses’ integrity after what amounted to allegations of insider trading, that employees were placing bets using information not generally available to the public. The statements were released after an employee at DraftKings, one of the two major companies, admitted last week to inadvertently releasing data before the start of the third week of N.F.L. games. The employee, a midlevel...