Bousouzoku (暴走族) (literally "speeding tribe", known also as kamikaze bikers) is a Japanese subculture very similar to car clubs: gangs of young men who share a common interest in designing (often law-breaking) modifications to cars and motorcycles.
Among their activities is shinai boso: it consists of driving down the streets at high (illegal) speeds. It is not properly a race; mostly, it's done just for the thrill of it. With many cars (or bikes) involved, the leading one is driven by the sento sha (the leader), who is responsible for the event. Nobody is allowed to overtake him. Others keep a lookout for side and rear cars/bikes.
Bousouzoku members tend to be perceived as criminals and misfits, and they are commonly said to be recruiting grounds for the Yakuza, but mostly that is only the impression they want to give. Actually, very few bousouzoku members are older than 20 years and it's assumed that their activities are a way to relieve the teenage stress.
See also
