It is brief and to the point, not a detailed medical analysis of an injury. Therefore use the information accordingly. Jon is the Coordinator of Athletic Training at Stockton. He obtained his undergrad degree at William Paterson University and his Masters degree at the University of Florida. But we've stuck to our guns here at Stockton, we still use the TSS identifier.
Speculation is rampant, but in reality no one really knows.
It may be irritation of the outer covering of the tibia itself, tendinitis of the muscles of the lower leg, or a combination of both. It also could be any of several other possibilities. In most situations the athlete will have pain on the posterior-medial aspect of the tibia. Normally the painful area will be 2-5 inches in length. TSS is an overuse injury.