This refers to inflammation of the tendons for the calf muscle at the back of the knee. It is an overuse injury where microscopic tears accumulate in the tendon faster than the body can repair them, and inflammation results.
Pain is felt at the back of the knee and may be associated with tightness in the calf. It usually starts gradually and may only be painful after exercise initially, and going away as you warm up. As the condition progresses the pain may become more intrusive, interfering with participation, or occurring at rest.
If you think you have this condition it is well worth getting it checked out by Mr Willis-Owen. In the mean time you should avoid any aggravating activities which may prolong the problem. It generally won't get better on its own. The first thing to do is to reduce the problem activities, and start a concerted program of calf stretching. Anti-inflammatories and ice are helpful after exercise.
Treatment involves first confirming the diagnosis then establishing the cause. An ultrasound scan or MRI scan can be useful to exclude other problems. Treatment options may include specific physiotherapy, or injections. Once you have recovered, good physio should be able to prevent this from coming back.