In soccer, sports science aims to prevent injuries and improve performance by biomechanically analyzing a series of the kick processes. In order to understand the kick processes biomechanically, studies on kinematic, kinetic, and EMG have been conducted. However, these studies have limitations due to absence of integrated theory defining interactions between the segments. In the present work, we propose a model to understand dynamic characteristics of the kicking leg based on the biomechanical features of the instep kick. Five healthy men participated in an experiment to perform four-level instep kick. We collected kinematic and kinetic information of the hip and knee joints. Based on the passive dominance of the knee joint, we devised the knee joint torque model proportional to angle and angular velocity. RMSE between simulated and real torque was 4.17%, and exhibited a tendency to decrease linearly with the kick speed. Henceforth, it is apparent that the faster the kick, the greater the load on the hip; and the slower the kick, the greater the load on the knee joint. We anticipate that this model will be applied to the kick monitoring equipment and for the prevention of injuries by measuring the load.