After the Olympic 800m final at Rio de Janeiro in August 2016 the BBC broadcast interviews with two of the competitors. South Africa’s Caster Semenya spoke matter-of-factly about a victory that was expected. Then the sixth-placed finisher, Scotland’s Lynsey Sharp, stood before the camera. The two minutes that followed were a jolting insight into the complexities of what should be sport’s most simple contest: a two-lap running race.

An Olympic final was surely the highlight of Sharp’s athletic life. That was not how she felt. “I have tried to avoid the issue all year,” she said when asked about Semenya’s victory. To those unfamiliar with track and field, it seemed something was wrong. To the rest of us, it was obvious. At the end of