Could be a number of things, ACL, LCL, meniscus.
So, I've had ACL reconstruction. During the injury, I felt a sharp pop and limited mobility. After the injury, maybe an hour later, the knee started swelling up, like a grapefruit size and I could hardly bend it.
After the swelling went down, the pain went away, but every once in a while, when I turned, I could feel a sharp pain inside the knee.
So, my doctor told me to come back in a week after the swelling goes down, because the swelling could also be affecting the pain and would not provide an accurate X-ray. So, I waited. The swelling did go away. The pain was still there so I went in. I got an x-ray and physical examination. Then, he said I would need an MRI to get a better view of the insides.
So, you do need to take some time for the swelling to go away to see if the pain persists afterwards. You said you got injured in a game one night ago. Once the swelling goes away, your pain symptoms may change or go away or stay the same. Ice it. Take it easy. After a week, the swelling should go away and pain level should decrease, you can probably resume your usual activities. See how your knee feels. If pain persists, see your doctor again. Note when pain occurs, going up steps, going down steps, running, standing, kneeling, turning, jumping, kicking, bending, certain angles, leg fully extended, etc. and tell that to the doctor.