Plantar fasciitis is when the plantar fascia ligament is strained causing pain at the bottom of your foot. The plantar fascia is a ligament-like band running from your heel to the ball of your foot. This band pulls on the heel bone, raising the arch of your foot as it pushes off the round. If your foot moves incorrectly, the plantar fascia may become strained. The fascia may swell and its tiny fibers may begin to fray, causing plantar fasciits.