When the ACL is injured it can cause pain, swelling and a feeling of the knee 'giving way', making it difficult to bear weight or participate in activities - particularly sport. Scenarios that commonly lead to ACL injuries in football include rapid directional changes and landing after heading the ball.

The NFL has implemented rule changes in recent seasons aimed at reducing lower-body injuries, including the ban on hip-drop tackles. Still, experts say the nature of the sport, built on speed, power, and rapid changes in direction, means ACL injuries remain a risk.