Most of the time, shin splints are caused by increasing your training by running too much or too fast. If you are a beginning runner, it's usually from starting out too aggressively, building your mileage too fast, not getting enough rest time in, or doing too much speed work.
In experienced runners, shin splints can be caused by changing flat runs to hill work, too much speed work, changing footwear to a new manufacturer, not changing running shoes frequently enough, or adding too much mileage too soon.
The most common area of pain in shin splints is the medial area or inside the shin bone. The common consensus is that there are micro-tears in the muscle where it is pulled off the bone, which then tears the covering of the bone creating a periostitis. The nerve fibers and blood supply in the periosteum is very extensive, therefore disruption of that area results in sharp pain.
Continual tearing by running or any sport will create sharp pain and disability, which will not go away without rest. Anterior shin splints have a number of specific causes.
Sometimes, athletes that have a restriction that prevents the ankle joint from flexing (when the top of the foot gets closer to the shin) the muscles in the front of the shin actually have to lift the foot to prevent tripping. This creates an overuse injury and then shin splints.
It's also worth noting that shin splints can be caused by tight calf muscles preventing the ankle from bending properly.