As you are a sportsman, the knee pain
could be most likely due to trauma
. If you notice a click in a typical position of the knee, it could be a meniscal injury. If your knee locks, i.e gets stuck suddenly while extending it, again it could be related to meniscal injury or a loose body. A loose body can arise from a separated piece of cartilage
with or without bone attached to it due to previous trauma. In this case your knee may lock in a different angle every time, unlike for meniscus
where it always locks in the same angle of knee flexion
If your pain doesn't subside with rest, analgesics and appropriate physiotherapy, you will require an Orthopaedician's (Arthroscopy surgeon) opinion, an MRI and/or diagnostic Arthroscopy.
An MRI or diagnostic arthroscopy will reveal the problem with your knee.