Soreness inside the knee after playing soccer may be caused by over-exercise, knee synovitis, meniscus injury, etc. It is recommended to consult a doctor in time to find out the cause of the disease. 1. Excessive exercise: after a long period of strenuous exercise, the accumulation of lactic acid produced by the muscles leads to soreness and pain in the knee joint. 2. Knee synovitis: Knee synovitis is a sterile inflammation caused by acute trauma and chronic injury to the knee joint. Abnormal function of synovial membrane will lead to the joint fluid can not be generated and absorbed normally, the knee joint will produce fluid, resulting in knee joint soreness and swelling, pain and accompanied by activity limitation. 3. Meniscus injury: Meniscus injury caused by trauma or degenerative injury will lead to knee pain. If there is pain in the medial joint space of the knee when jumping, running or squatting, or pain in the lateral joint space, it is usually due to the damage of the medial meniscus of the knee, or the corresponding lateral meniscus. 4. Other reasons: If there is an old injury of the cruciate ligament, the patient will also have soreness when playing basketball and other strenuous sports. Soreness inside the knee after playing basketball may also have other causes, such as rheumatoid arthritis, etc., such as rest after the symptoms have not improved, it is recommended to consult a doctor in a timely manner, a clear diagnosis, under the guidance of the doctor for targeted treatment.