A muscle does not need to be maximally stretched to be torn.
Muscle tears are the consequence of a combination of a sudden contraction and a stretch at the same moment.
Large differences in strength between two opposing muscle groups (e.g. quadriceps and hamstrings), unilateral strength imbalances (left leg vs right leg) as well as a difference in muscle endurance between the limbs are the leading causes of injuries.
Developing the strength and endurance of deficient muscles is the best injury prevention method. A movement analysis may also useful to prevent injuries.
Good technique should feel effortless. The moments in a technique where maximal strength of already stretched muscles is used to counteract the quick movement of a big mass should be abandoned.
Such movements may cause muscle tears in the supporting leg during kicking, for instance. Good flexibility on its own cannot prevent injuries.
If one muscle group, or the muscles of one side of the body are more tensed than other muscles, it may be an indication of a nerve issue or misaligned bones.
For instance, a twisted pelvis will lead to one hamstring being more tensed than the other. Stretching excessively tensed muscles will not fix the cause of their irregular tension. In this instance, it neither realigns the pelvis nor focuses on this misalignment, which could be neurological or mechanical.
While stretching can make oneself temporarily feel better, it will not remove the risk of possible injury. This is why static stretching before training will not prevent injuries.
