Overstretching sideways can cause hip abductor strain, and overstretching forwards with the leg to kick the ball can cause a hamstring strain. Shin injuries from idrect kicks can cause a fracture of the tibia. Shin guards are important to prevent this injury. Knee sprains and ankle sprains are very common soccer injuries. This causes impingement syndrome and pain with the upstroke due to the rotator cuff being impinged by the acromion and coraco-acromial ligament.
Treatment consists of rest, ice and antiinflammatory medications.
Prevention includes learning proper technique, or learning an alternative swimming style. Breast-stroker's knee is due to the whipkick that puts excessive strain on the medial collateral ligament of the knee. By reducing the width of the kick, this problem can be avoided. Back pain can occur with the butterfly stroke, and is due to strain on the back. Reduction of training and alternating swimming styles while training may help.