Change-over rules for women's team sprint
The rules for Track Races are here. In the Team Sprint:


  The leading rider shall lead the first lap and move towards the outside of the track and then drop back to leave the track without hindering the other team.


In Great Britain's semi-final this is what happened at the end of the first lap:



Jess Varnish (nearest to us in the picture) was the leading rider with Victoria Pendleton as the second rider. Jess Varnish should have lead for the whole of the first lap, unfortunately Victoria Pendleton overtook her before the first lap was completed and they were disqualified.

The same thing happened to the Chinese team in the final.