10 August 2012 Last updated at 16:25

Olympics BMX: Five riders tumble at the first turn

French BMX rider Quentin Caleyron's mistake causes a five bike crash in the first bend of a gruesome opening semi-final heat.

Britain's Liam Phillips escapes unharmed to take second place behind Connor Fields, the same man he was runner-up to in the quarter-finals.

You can watch the full session on our interactive video player.

Available to UK users only.