This large strap like band travels from the outside of the hip down along the outside of the leg and attaches onto the outside of the knee. This band will get injured if it is tight, if the foot over pronates, there is a leg length difference, or there is weakness in the hip and core muscles, which all allow the knee to collapse inward. These things can put increased stretch and tension on the band, where it usually gets irritated down at the knee area. It rarely gets red or hot, but it will be sore with some stair climbing, lunges or running. It will feel better with cessation of running, but as always, treatment should include correcting any misalignment of the hips, and feet, as well as strengthening the leg/hip muscles.