Excessive tension on the Piriformis can irritate the Sciatic nerve. This may lead to pain or nerve irritation in the buttocks, hamstrings, lower leg and foot.
Excessive tension in the Piriformis can also externally rotate the hip, leading to poor movement in the hip.
The Piriformis muscle originates on the front of the Sacrum and inserts on the top of the Femur. The Piriformis is responsible for external rotation of the hip below 60 degrees of hip flexion. Above 60 degrees, it becomes a hip internal rotator.
You can release excessive tension in the Piriformis with a foam roller:
Sit on the roller with your hands behind you on the ground and the soles of your feet resting on the floor.
Lean to your left side, take your right hand off the ground, the place your left ankle on your right knee.
From the starting position, roll back and forth over the piriformis.
Roll for 30–60 seconds, and then switch sides. Try altering your body position throughout to approach the piriformis from multiple angles.
To increase the pressure further you could use a harder roller or use a medicine ball which isolate the pressure to a smaller area.