According to Wikipedia: "Cycle ball, also known as "radball" (a German word literally translated as "wheel-ball") is a sport, similar to football only the competitors play while riding bicycles. Each of the two people on a team rides a specialized bicycle with no brakes and no freewheel (a fixed gear bicycle). The ball is controlled by using the bike and (rarely) the head, except when defending the goal."
That is one of the craziest sports I have ever seen!! I don't know how they do it...