There is a hard lump in the callous of the ball of my foot, what is this?

Need exam: It is very difficult to say without seeing and examining the foot. The hard lump may be a prominent bone such as the head of a metatarsal, it could be a tumor, it could just be part of the callous itself. See your pcp or podiatrist for evaluation and treatment.

Intractable plantar: Some calluses which are very thick are called intractable plantar keratosis (ipk). Ipk's are discrete, focused calluses usually found on the ball of the foot. They can be shaved down by a foot doctor but will return in time.

Many possibilities: Some causes of “lumps” may include: bony overgrowths, soft tissue masses, ganglions, fibromas, cysts, and infection. Have it evaluated by a professional to get the right diagnosis.