The knees collapsing inward during squats, jumps and landings. One of the key risk markers in technique analysis.
When the knee drifts inward while the foot stays put, the ACL takes shear load — especially on single-leg landings. The cause is rarely the knee itself: usually the glutes and hip external rotators are too weak to hold the femur, or the arch of the foot collapses along with it. Important when filming: valgus is a frontal-plane measurement. Shot from the side you only see the projection of knee flexion, which makes the value meaningless. That's exactly why the DOMISPORTS coach checks squats and lunges from the front.