Knee pain in young athletes is one of the most common reasons for a visit to a sports medicine clinic. The good news: most of the time, it is not a serious injury. The framework below will not tell you what is wrong, but it will help you describe what you are feeling more clearly.
Where is the pain? Pain on the front of the knee — especially just below the kneecap — has a different set of common causes than pain on the inner side, the outer side, or the back of the knee. Pain that is hard to localize ("all around") is often more diffuse irritation; pain that feels like a single point is often more structural.
When did it start? A sudden moment of injury (a twist, a hit, a hyperextension) suggests something different from pain that built up over weeks. Sudden onset with a pop and rapid swelling deserves an in-person evaluation soon. Gradual onset that worsens with running and jumping is the classic picture for overuse patterns.
What makes it better or worse? Pain that is worst during activity and eases with rest tends to be a load issue. Pain that wakes you from sleep, or pain that is present even at rest, is more concerning and should be evaluated.
Two patterns specifically worth knowing about in growing athletes: Osgood-Schlatter (anterior knee pain just below the kneecap, often in athletes 10–14 who jump or sprint a lot) and patellar tendon overuse (jumper's knee). Both usually respond to a temporary load reduction and a structured return to play. Neither is something you should try to push through.
If anything in your situation feels off — your knee gives way, you cannot bear weight, you have rapid swelling — stop the activity and see someone. The cost of an unnecessary visit is small. The cost of pushing through a structural injury is large.