Chat with Support and reference this article. 
Please include the following information and the Sphere Database team can restore.  Please note: this is a billable request.
  • Account Name
  • Event Name
  • Event URL
  • Company Name (if applicable)
  • Facility Name (if applicable)
  • Department Name (if applicable)
  • Team Name (if applicable)
  • Team Captain Name (if applicable)
  • Team Leader's supporter ID

  Typically, this prevents back end registrations.  Users can register through the front end of the site as a workaround.