Playing ball sprain knee has swelling and pain, proving that there is an injury, there may be muscle or ligament damage or contusion, to immediately stop sports, stop playing ball. Generally within 48 hours it is best to apply a cold compress, which is a plastic bag with ice, then wrap a towel and apply a cold compress locally to reduce the bleeding and swelling in the acute phase. After 48 hours, you can apply hot compresses or do physical therapy, do heat therapy and other irradiation to activate blood stasis, reduce swelling, and reduce the symptoms of swelling and pain. The sprained knee should be able to recover within 2 weeks. If it does not heal after 2 weeks of rest, the damage may be more serious and there may be a fracture, so you should go to the hospital for a specialist examination and take the appropriate treatment according to the examination results.