A method for determining whether a goal is achieved by a trajectory of a ball using a mobile computer device comprises capturing a sequence of video frames of the ball with a camera of the mobile computer device; detecting the ball in at least three of the video frames; computing a trajectory of the ball using the detections of the ball; detecting a goal image in at least one of the video frames; computing whether the trajectory of the ball achieves intersection or similar with a goal plane computed from the goal image according to a goal criterion.