I play volleyball and i noticed that my right knee feels tight. whenever i like stretch, squat or bend it its tight. what could it be?

Effusion in knee : Sometimes with minor trauma or from repetitive use, the lining of the knee joint or behind the knee cap can develop an effusion or fluid, similar to a water blister after friction trauma to the skin. If the knee hurts with walking and jumping or feels hot with touch, you should rest it and have an evaluation. If no pain, try cold compresses and decrease activity for a few days.