This is a pain you feel just below your patella (the bone we commonly call the "kneecap"). It's an injury to your patellar tendon, which connects the bottom of the kneecap to the shinbone.
You can injure your patellar tendon if you stress it. That can happen if you do a lot of physical activity that involves running or jumping. Other problems, such as tight thigh muscles, tight hamstrings, or a muscle imbalance of the leg can also cause a tendon injury.
This injury causes pain between your kneecap and your shin. It hurts more with activity. It may hurt so much that it's hard for you to get up out of a chair or to walk up stairs.
Treatment options may include rest, ice, medications and physical therapy. You may benefit from a support strap to brace your knee. If these aren't helpful, you may benefit from injections or from surgery. Your healthcare provider can create a plan that's right for you.