Recently I had knee injury and didn't see a physician but on the side of patella there is a hard thing popped out what is it? Ligament? Bone? Cruciate?
See a physician. Without knowing the type/mechanism of injury and whether you have other symptoms it would be hard to speculate. There are several possibles, but with a mechanical symptom of something hard next to the patella it is time to have a physician obtain a thorough history, examine your knee and possibly obtain x-rays or other studies.
Patella injury. It depends on the type of injury and depends in which side of you patella. I guarantee you that it is not your acl. It could be some scar tissue forming over the area if actually fell in your kneecap or it could also be a fragment of vaulted bone. If it continues to bother you you should have an orthopaedist actually examine you to tell you exactly what is going on. Tough without history or exam.