Might be worth looking at the psoas length and function in relation to the pelvic position. Mobilising the femoral trunk might ease symptoms in sitting. Try it and see. This could be a case where repeated flexion is a beneficial movement rather than the commonly used extension. Check also for pain in the inguinal area to rule out conjoint tendon or hernia issues.

Also what was the sport and is this the stance leg or the 'kicking leg'?