The “hip” is a ball-and-socket joint. It allows the upper leg to bend and rotate at the pelvis and gives a stable .  “Hip” fractures are considered to be fractures of the thighbone(femur), fractures of the socket(acetabulum) are a completely different consideration, please see Pelvic Fractures.  Hip fractures are either caused by large forces on normal bone, eg motorcycle crashes, or low forces on weaker bones, eg simple falls in the elderly.  Both can have significant long term consequences and need to be treated as soon as possible.