Pain in the buttocks half connected to the leg may be caused by lumbar disc herniation, pyriformis syndrome, lactic acid buildup and other reasons. 1. Lumbar disc herniation: prolonged poor sitting posture and other factors, resulting in lumbar disc herniation, compression of the sciatic nerve tissue, may lead to buttocks half with leg pain. 2. Piriformis syndrome: it is a disease caused by the compression of the sciatic nerve by the piriformis muscle, which may aggravate the compression of the sciatic nerve when walking, and then radiate to the leg, causing the patient to have the symptom of pain in the buttocks half of the leg. 3. Lactic acid buildup: If you do not exercise for a long time, but suddenly engage in strenuous exercise, it may cause lactic acid to build up in the buttocks and legs, resulting in pain in the buttocks and legs. The pain in the buttocks and legs can also be caused by other reasons, it is recommended to go to the hospital in time and follow the doctor’s instructions for treatment.