Any training program should apply the five basic laws of training to ensure improvement and keeping athletes free of injury. This is especially important for the young player. Most strength training exercises use the entire range of motion of major joints, especially the knees, ankles, and hips. Good joint flexibility prevents strain and pain around the knees, elbows and other joints. Ankle flexibility should be a concern for all athletes, especially beginners.
Good flexibility prevents stress injuries.
You must start developing ankle flexibility during prepubescence and pubescence so that in latter stages of athletic development it need only be maintained. Your muscle strength improves faster than tendon and ligament strength. Sometimes lack of a long term view or improper use of the principle of specificity cause coaches and trainers to overlook the strengthening of ligaments. Tendons and ligaments grow with anatomical adaptation. Without proper anatomical adaptation, strength training can injure the tendons and ligaments.