Calluses under the ball of the foot are often due to abnormal loading of the foot during push off. Like all calluses, the exact cause is excessive friction on the skin.
Calluses under the big toe or inside ball area indicate a rigid functioning segment that may need padding. A broad callus in the center is probably due to a non-functional inside column of the foot behind the big toe. This area has the larger bones and is designed to take larger loads. If the inside column isn’t functioning properly loads get shifted to the smaller bones in the central ball.
How Footwear Can Help
Reducing the thickness of the callus with a pumice stone can alleviate the discomfort, but the best approach is to address the abnormal mechanics with a proper shoe and a foot orthosis fitted by a podiatrist to control the motion of your foot and reduce the pressure on the ball of your foot.