In this paper, we propose a system for automatic judgment of offsides in soccer games. We detect and track players in fixed multi camera images and calculate the world coordinates of them. Furthermore, we do a formation analysis by classifying uniforms and calculate the position of an offside line. On the other hand, we calculate the 3D coordinates and the trajectories of a ball in world coordinates from the plane coordinates of a ball in multi cameras and recognize the moment of a play from the 3D trajectories of a ball. In addition, we make a judge player's interfering with play by analyzing the spatial relationship between a ball and players. Finally, we make an offside judgment by integrating these results. We apply our system to a real soccer match and demonstrate the availability of this system by showing the experimental results.