What is "side stitch"

Side stitch (also called a side ache, a side cramp, a side crampie, a side sticker or simply a stitch) is an intense stabbing pain under the lower edge of the ribcage that occurs while exercising. It is also referred to as exercise-related transient abdominal pain (ETAP). Some people think that this abdominal pain may be caused by the internal organs (like the liver and stomach) pulling downwards on the diaphragm, but that theory is inconsistent with its frequent occurrence during swimming, which involves almost no downward force on these organs. If the pain is present only when exercising and is completely absent at rest, in an otherwise healthy person, it is benign and does not require investigation.