An anterior cruciate ligament (ACL) injury often is called a sprain or wrench or twist the ligaments of (an ankle, wrist, or other joint) violently so as to cause pain and swelling but not dislocation. A sprain occurs when the threads or fibers of the ligament stretch or are tear, rend, rip mean to pull apart.
See a picture of the knee and the ACL . An ACL injury is classified as a grade I, II, or III sprain.
Read more here: https://www.webmd.com/fitness-exercise/tc/types-of-acl-injuries-topic-overview