Types of tears: functional or non-functional
Several different words are used to describe a torn ACL including ruptured, snapped, injured, torn and popped for example. Once injured, it can partially heal in some people and this may give sufficient restraint to return to non pivoting sports. In most however, the ligament will not heal tight enough to function for sports involving rapid change of direction.
The principle, therefore, is whether the cruciate ligament is functional or not functional in controlling stability in rotation activities. If the ligament is functional and the requirement to get back to fast pivoting sports is low, then surgery is not likely to be needed.