What could cause severe hip pain?

Many things: Here is the list - osteoarthritis, gout, strain, labral tear, inguinal hernia, sports hernia, avascular necrosis, bone contusion, tendonitis/bursitis, pinched nerve in lower back, etc. As you can see, the list is pretty long. Remember, common things are common, so things like arthritis, strains/sprains and tendonitis tend to top the list. Lastly, see your physician if the pain persists.

Probably arthritis: Get it evaluated and x rayed and then you will know.

Multiple causes: Hip pain can be from a number of causes in the joint, around the joint, or referred from the back. It is important to see an orthopedist who treats hips A through history and exam is needed. X-rays and possibly an MRI arthrogram may be ordered.