Piriformis muscle is within the buttocks. It assists in hip stability and almost every motion of the hip joint. Improper biomechanics can cause shortening of this muscle which will in turn compress the sciatic nerve giving pain in the gluteal region.
Sciatic nerve runs from your spinal cord to your buttock/hip area and down the back of each leg. Irritation or compression anywhere along this nerve will give radiating pain downward.
IT Band Syndrome
IT band is a long tendon that runs from the hip to the knee along the outside of the thigh. It aids in stabilization of the hip and knee. Improper biomechanics at the hip or knee can lead to friction at either joint respectively.