The purpose of this study was to determine the relationships between pelvic motion during the READY phase of the Taekwondo roundhouse kick and the actual kicking speed and time. Understanding these relationships will provide greater coaching and training opportunities to improve athletes` success in scoring points with roundhouse kicks time. It was hypothesized that the contribution to kicking speed and time from the connective joints adjacent to the pelvis would be explained by the mechanical energy generation, flow, and transfer determined through kinematic and kinetic analyses. Thirteen (13) male Japanese Taekwondo athletes participated in this study. The results were summarized as follows: 1) the key factor to transfer the mechanical energy to pelvis efficiently is to establish the posture quickly as it is easy for the extension of hip joint in the support leg, 2) the motion timing of the hip joint in the support leg was quite different between the GOOD and POOR groups, 3) the GOOD athletes utilized the techniques of pelvic motion in the support leg, 4) it is better to train a quick motion with a narrow hip joint movement range while in standing position, and 5) the Taekwondo player should feel as if they are pushing the hip joint of their support leg and moving the pelvis in the kicking direction to facilitate the mechanical energy transfer in order to kick faster. Taken together, the data suggested that coaches should pay greater attention to the support leg and the READY phase in order to improve the players` kicking speed.