Piriformis syndrome/Sciatica

The piriformis is a muscle deep in the gluteal/buttock area.  Tension in this muscle and surrounding muscles can cause compression of the sciatic nerve causing pain in this area, around the hip and also down the leg.
Massage and mobilisation of the leg, hip, glutes, piriformis and lower back muscles has a great effect in reducing this tension and reliving the compression and reducing pain.

Groin Strain

This is pain in the inner thigh due to a tear in the muscle attaching to the inner groin.  This tends to be a sports injury and is a result of running, changing direction quickly, or kicking a ball.
Gentle massage of the area can increase blood circulation and reduce inflammation/tension of the muscles in that area.