Shares of UnitedHealth Group ( UNH -14.89%) are falling on Thursday. The company's stock has plummeted 15% as of 11:33 a.m. ET but lost as much as 19.2% earlier in the day. The collapse comes as the S&P 500 gained 0.1% and the Nasdaq Composite fell 0.4%.

Stephen Hemsley hasn’t been CEO at UnitedHealth Group in nearly a decade yet he’s never really left. Hemsley, 72, has remained chairman and a major shareholder in the health care behemoth — and now is back in the CEO

Amedisys (NASDAQ:AMED) earlier ticked down 0.2% on a report that the Dept. of Justice has initially rejected the proposed divestiture buyers for its planned sale to UnitedHealth (NYSE:UNH). The DOJ hasn't been convinced that the remedy proposal,

Stephen Hemsley ran UnitedHealth Group for more than a decade. It's a different company after four years with Andrew Witty in charge.