1. Data Stadium, What is the batter's "type"?, Baseball Lab Editorial Department, available from <http://www.baseball-lab.jp/column/entry/1> (accessed on 20 February, 2020) (in Japanese).
2. Japan Sports Agency, About the present conditions of athletic club activities, available from <http://www.mext.go.jp/sports/b_menu/shingi/013_index/shiryo/__icsFiles/afieldfile/2017/08/17/1386194_02.pdf>,(accessed on 21 February, 2020) (in Japanese).
3. Kageyama, M., Suzuki, T., Fujii, M., Nakamoto, K. and Maeda, A., A cross-sectional study on swing characteristics of baseball players, Proceedings of Health and Sports Science Conference (2016), p.268 (in Japanese).
4. Kidokoro, S. and Yanai, T., Characteristics of swing affecting flight distance and kinetic energy of the ball immediately after impact in baseball batting, Journal of Biomechanics in Sports & Exercise, Vol.15, No.3 (2011), pp.78–86 (in Japanese).
5. Kidokoro, S. and Yanai, T., Two mechanisms of ball impact that determine the horizontal direction of batted ball velocity in baseball: Their contributions to batted ball speed, Journal of Physical Education, Health and Sport Sciences, Vol.62, No.2 (2017), pp.475–490 (in Japanese).