Just wondering while watching football - do they have substitute referees/linesmen? I imagine a lines would be promoted if a referee was injured or taken ill, but who would then replace the linesman?
A fourth official is often also a referee and can take the place of any of three match officials (referee, two assistants) if they cannot continue for whatever reason.
Are all officials 'equal' ie can a linesman (or assistants as they now seem to be called) be a referee or do they have to earn promotion eg by exams or assessments?