Dear most probably ur suffering from anterior crucial ligament injury which is very much common in sport person . It occurs moat commonly whule playing either due to sudden rotation of knee or due to trauma from lateral side. As injury is to soft ligament xray finding will be normal. In symptoms u will have high swelling along with instability of knee leading to difficult walking and difficult bending. The complete torn ACL may lead to complete loss of stability of knee. For diagnosis only arthroscopic examination can diagnose it...ACL repair can be done y arthroscopy. I recommend u to visit a good orthopedic surgeon asap. Thanks Revert back for follow up.