Ischial bursitis is the irritation of the bursa at the bony prominence behind the pelvis, called ischial tuberosity. This bony prominence represents an insertion zone for several muscles, including the hamstrings, and provides support in the sitting position.
Activities and sports that require the hamstring muscles to be repeatedly contracted or stretched during running, jumping or kicking can cause irritation of the bursa and sometimes inflammation. Ischial bursitis usually results from injury to the hamstring tendons. Prolonged sitting on a hard surface or falling on the buttocks can also aggravate the irritation.