Abstract: There is provided a method and a system for registration of real time position of tennis ball relatively to boundary lines on tennis court. The method and system comprise sensitive to near-infrared radiation at least one video camera, outputting video image of court and the method and system further include at least one point source of near-infrared radiation, illuminating tennis court and displaced relatively to the video camera. It is suggested a simple and inexpensive way of determining if a tennis ball bounces in or out of court by determining point of intersection of trajectories of the tennis ball and its shade from near-infrared radiation and comparing the position of the determined point of intersection with previously calibrated boundary lines of court.