Acetabular labrum tear is a common finding in the aging adult hip and is also associated with TRAUMATIC injury, usually caused by the hip joint being stressed in rotation. The pain is mainly felt in the groin (but can be in the trochanteric or buttock region) and is commonly SHARP, with a CLICKING and catching sensation. Activities that involve break down adduction of the hip joint in association with rotation in any direction tend to aggravate the pain.
http://www.pponline.co.uk/encyc/acetabular-labrum-tears.html

If its not a tear, then consider arthritis…
If arthritis narrows the hip joint or impinges on the way the femoral head can glide in the acetabulum, or if there is a cartilage or labrum tear, the pain may be associated with a “catch,” or a suspicion like there is something impeding hip movement.
Pain from arthritis tends to be worse after a period of inactivity and gets better as the joint “warms up” with use. But as activity increases, the pain will return.
http://www.emedicinehealth.com/hip_pain/page2_em.htm

Read on Acetabular dysplasia too.

Femoral acetabular impingement
http://en.wikipedia.org/wiki/Femoral_acetabular_impingement

http://www.emedicinehealth.com/hip_pain/page7_em.htm#medical
http://www.emedicinehealth.com/hip_pain/page8_em.htm#medications
http://www.emedicinehealth.com/hip_pain/page10_em.htm#prevention