# Biomechanical Characteristics for Identifying the Cutting Direction of Professional Soccer Players
## 4 Discussion  
### Characteristics That Determine Soccer Players' Cutting Movements  
This study found that when a soccer player cut in different directions, the body showed different movement characteristics, so the defender can predict the attack direction through the height of the hip joints and rotation direction and adduction or abduction of the ankle joints. The results of the attacker's cutting decision distance and speed were the same in the two cutting directions, i.e., the attacker would choose to cut 1.2 m from the defender. The run-up speed of the attacker can reach 3.1 m/s. After the cutting foot lands, body speed will decrease to 2.6 m/s. From the run-up to the landing of the cutting foot, the height of the body (hip joints) will decrease by about 6 cm.  
Previous research and analysis on soccer players' cutting movements found that the foot will show a relatively large version angle when cutting in the direction of the customary foot [9], and the knee joint angle will change significantly at the initial stage after the landing of the supporting foot during the cutting movements [14], so the attacker's intention to cut can be predicted by observing the joint motion. The results of this study show that the defender can predict the cutting direction chosen by the attacker by identifying the angles of adduction and abduction of the attacker's foot and the height and rotation angle of the hip joints, among which the angles of adduction and abduction of the foot provide good directivity, as it is easy to observe the difference in such angles. Defenders can observe the heel-toe position of the cutting foot for identifying the intention of cutting direction. When the attacker cuts to the right, the cutting foot (front foot) presents the regular characteristics of abduction, which is 7\({}^{\circ}\) different from the angle when cutting to the left. When the attacker's cutting foot lands, if the defender recognizes that the attacker's front foot is abducted, it can be presumed that the attacker will cut towards the right, and if the front foot is adducted, then the attacker will cut towards the left.  
According to the gait model established by [PERSON] and [PERSON] [14], when the hip joints rotate, the ankle joints also rotate. [PERSON], [PERSON], and [PERSON] [15] found that hip joint angles will affect the position of the cutting foot from the body centerline, so when the hip joint movements change, the ankle joints also change, which affects the direction that the feet point. When the attacker cuts to the right, the hip joints have a relatively large internal rotation angle; however, when the attacker cuts towards the left, there is little internal rotation action. In sports biomechanics, the position of the center of mass is used to indicate the movement of the human body. However, during competition, it is difficult for the defender to identify the position of the center of mass of the attacker (the height of the center of mass is difficult to judge by vision). The hip joints are close to the height of the center of gravity, and their position is close to the junction of the pants and shirt, which is convenient for the defender to identify and judge. Observing the changes in the height of the hip joints is one of the methods used to predict the cutting direction of the attacker.