sentences:  His victory at the Dutch TT in Assen together with an eighth-place finish by Roberts, vaulted Ferrari into the championship lead as the series headed towards Belgium.Ferrari became embroiled in a controversy at the Belgian Grand Prix held at the Spa circuit when he, along with Roberts and other top riders refused to race due to unsafe track conditions.The circuit had been paved just days before the race creating a track that many of the racers felt was unsafe due to diesel seeping to the surface.