Basic study on appearance-based proficiency evaluation of the football inside kick

We are developing an appearance-based proficiency evaluation system for individual fundamental football skills. As a basic stage of the research, we propose a method to discriminate between beginners and experts based on features of the inside-kick motion, which is a fundamental skill in football. In addition, we propose a method for scoring the inside-kick motion. To provide ground truth, a football coach (former professional football player) scored a series of inside-kick trials based on five criteria. Each criterion was scored out of 20 points, resulting in an overall score of up to 100 points for each trial. We utilized dense trajectories to extract features from the inside-kick motion and bag of features for feature vectorization. A random forest was then adopted to remove the effects of individual techniques from the feature vectors. Finally, a support vector machine was utilized to discriminate between beginners and experts. Each trial was evaluated based on five criteria to score the inside-kick motion using support vector regression. Total score estimates were calculated as the sum of the scores for each criterion. The results reveal that the accuracy of beginner/expert discrimination reached a maximum value of 91%. The average difference between the scores estimated by the proposed method and those rated by the football coach was approximately 0.17 points. Overall, these experimental results confirm the effectiveness of the appearance-based proficiency evaluation system.