The ball of my foot is swollen. what could it be?

It could be: Sesamoiditis, this is a small bone under the first metatarsal head, it could be capsulitis, it could be a stress fracture, it could be a sprained joint. Gout is another possibility. Ice would help all of the above except, i don't recommend ice for gout. Try an antiinflammatory as well. If still problematic visit the doc who will be able to x-ray your foot and better evaluate you.

Neuroma or fracture: The most probable causes of the ball of the foot being swollen are a morton's neuroma, gout, or a stress fracture. Physical exam by your podiatrist and an x-ray will determine which of the above is your problem.

Stress fracture: Bursitis, metatarsalgia. Tendonitis. Go see tour podiatrist.

Injury/inflammation.: Possible stress fracture, contusion or other type injury as well as infection, gout or arthritity.

Swollen: As you can see from the other answers , there a number of possible causes. See your podiatrist for an evaluation and determination of the cause and formulation of a treatment plan .