The most common cause of foot pain is certainly within the foot itself. People develop arthritis, bursitis, tendonitis, you can have a neuroma within the foot; there are a number of causes within the foot itself that would cause foot pain. Sometimes, however, the cause of foot pain is actually coming from the spine.
The same sorts of things that can cause pain radiating into the leg can cause just foot pain as well. This basically is stenosis within the spine. This can be caused from a number of different causes: herniated disc, spondylolisthesis, ligamentum flavum buckling, or hypertrophy of the facet joints, all of which have the same common denominator, which is basically narrowing of the hole where the nerve comes out of the spine and then a propensity towards developing inflammation around that nerve that can then send pain down into the leg. Typically when that happens, it sends pain down into the leg and it follows a course into the leg. But sometimes it can actually present as just foot pain, and often when that happens, there may be associated numbness, tingling, weakness, but sometimes it will be just pain, and it's important to consider that whenever you're evaluating the foot.