Our system involves a table tennis practice table where one-half of the table in the vertical position returns the player's shots. We use a digital projector calibrated with the table's vertical half, a digital video camera, and a vibration detector mounted on the table. When a ball strikes the wall, the vibration detector triggers the camera to photograph the wall. Our system processes the photograph and projects an image of the ball's impact location onto the wall. The system can also project statistics during play. We designed it to be low cost, to minimize setup time, and to maximize portability. We envisage that the system could work for many interactive games and sports, such as regular tennis, darts, and soccer.