Less spinning soccer ball aerodynamics are studied by wind tunnel experiments. Aerodynamic force of unsteady lift and side ones acting on the ball at rest are measured and estimated flight trajectory. Well agreements of flight shift magnitude in lateral direction between observed and calculated ones are obtained. Violent position change of longitudinal twin vortex just behind ball rear surface is observed using flow visualization method by high speed camera and smoke image method. As a result, the cause of this strange behavior of less spinning soccer ball is clarified by self-excited buffeting phenomenon of irregular behavior of omega Ω shaped vortex and longitudinal twin one, which already discovered with supper critical Re number region of smooth sphere by Taneda (1976). These twin vortices appearance are very similar to well known trailing vortices of both side of an air plain wings.
