The keirin is a 2000-meter track event where the riders start the race in a group behind a motorised derny. The derny paces the riders for 1400 meters and then pulls off the track, at which time the cyclists begin a sprint to the finish line. Keirin racing has traditionally been practised in Japan, where it has been a professional sport for over 20 years, and only in which pari-mutuel betting on the riders is permitted.