Im an 18 year old sprinter, I run the 100, 200, and 400. Last month, I started feeling a slight twinge behind my right knee. I ignored it (which I know I shouldn't have) for about 2 weeks until the pain started to get worse. My coach recommended a stretch for it (sitting down both legs parallel to the ground, wrap a rope around the mid foot and pull the upper body towards the toes, keeping the upper body perpendicular to the ground), which worked the first couple of times. After that, the pain returned, slightly worse, but I noticed that after one hard sprint, it would hurt a lot immediately afterwards, but the pain would subside after that, and after a couple more hard sprints, the pain would be gone. I then began to notice a visible tightness behind my knee that hurt upon massaging it. Massaged seemed to help lessen the pain. The pain is brought on especially by doing leg kick drills (while skipping, bring the leg up so that the upper leg is parallel to the ground, and then kick the lower leg out). Does anyone have any solutions for this problem? Thanks in advance