Plantar fasciitis is a common cause of stabbing pain under the foot. It is caused by inflammation of the plantar fascia, a thick band of tissue that runs along the bottom of the foot and connects the heel bone to the toes. Symptoms of plantar fasciitis include sharp pain in the heel or arch of the foot, especially when standing or walking. Treatment usually consists of rest, stretching and anti-inflammatory medications. In some cases, a heel spur may develop, an extra bone outgrowth on the heel bone that can cause additional pain.