Calf cramps with hard lumps may be caused by calf muscle strain, acute strains, calcium deficiency and other reasons. You should consult a doctor in time to find out the cause. 1. Calf muscle strain: prolonged walking or exercise can lead to overloading of the calf muscle stress, resulting in muscle strain and muscle fiber spasm, manifested as cramps and spasmodic pain in the calf, stiffness of the leg, pain can be more pronounced during weight-bearing activities, which can be relieved after rest. 2. Acute strain: insufficient warm-up activities before exercise, improper exertion, may lead to calf gastrocnemius muscle strain. Acute injury to the calf gastrocnemius muscle, there can be acute swelling of the calf, the injured muscle can be spasm, manifested as cramps in the calf stomach, hardening, can also be accompanied by subcutaneous bruising. 3. Calcium deficiency: Calcium ions are involved in inhibiting the excitability of neuromuscular joints. When the body is deficient in calcium, neuromuscular excitability increases, which often leads to cramps and hardness in the calves, usually occurring at night, and can be accompanied by cramping pain in the calves. There may be other causes of calf cramps, and you should consult your doctor in time to clarify the specific cause and treat accordingly if necessary.