That bony area on your pelvis that you feel when you sit? It's called the ischial tuberosity. Sprinters, hockey players and soccer players are especially vulnerable to IT or "sit-bone" injuries. IT injuries occur when your hip is forcefully flexed with the knee extended, such as while kicking, performing a split or hurdling. The injuries are typically caused by powerful eccentric (lengthening) contractions of the hamstrings and adductors or by repetitive use of these muscles.
Ischial tuberosity apophysitis is an inflammation where the tendons attach to the bone, typically resulting from repetitive stress to the area. It is usually seen with a gradual increase in pain with use, and tenderness without any major trauma at the time of injury.
An ischial tuberosity avulsion fracture, where the tendon pulls off a piece of the bone, is usually caused by a forceful muscle contraction. It brings a quick onset of pain, swelling and weakness. You will experience tenderness in the sit bone, and you will have difficulty walking and sitting for prolonged periods.
If that happens, you should see a sports health professional. Don't shrug it off as a "pulled hamstring" (hamstring strain). Perhaps because IT injuries are less common than hamstring strains, they are often misdiagnosed as a simple strain or pulled muscle. They usually heal with conservative therapy. However, the injuries may require surgery, and the longer a correct diagnosis is delayed, the more extensive the surgical procedure may be. Not all injuries require surgery, but information on the extent of an injury is useful in planning a rehabilitation program and a return to your sport. The quicker the injury is identified and treated, the less chance you will develop chronic pain or risk not returning to your prior level of performance.
Off-season and pre-season training programs that address muscle imbalances and flexibility could help you avoid this pain. It is also important to perform a proper warm-up.
Diagram Credit: Bickley, Lynn S.; Szilagyi, Peter G. Bates' Guide to Physical Examination and History Taking, 10th Edition. Copyright ©2009 Lippincott Williams & Wilkins.