An increasingly fierce court fight unfolding in Boston between a major health care company and a former senior executive who jumped to a new venture highlights the pressure established players feel when rivals show up and threaten to disrupt an industry.

The UnitedHealth Group Inc. subsidiary Optum sued last month to stop its former director of product strategy, David Smith, from working at the upstart venture involving Amazon, Berkshire Hathaway and JPMorgan Chase that promised to “address health care for their U.S. employees, with the aim of improving employee satisfaction and reducing costs.”