What actually tears the ligament
When people hear ACL they picture a tackle. The evidence is almost the opposite — most ACL injuries in football happen with no contact at all. They happen in the split second when a player decelerates, cuts, or lands from a jump, and the knee rolls inward toward the other knee while the foot stays planted. The sports-medicine people call that dynamic valgus, but you do not need the term. You need the picture: knee caving in, hip not holding it, bodyweight dropping through a nearly straight leg. Once you can see that picture on your field, you can start to coach it out.
Why I treat this as a development question, not a medical one
Here is the part that matters for me as a coach. If these injuries were random, there would be nothing for us to do and we could hand the whole thing to the physio. They are not random. The protection sits in neuromuscular control — how the hip, knee and foot line up under load, how strong the hamstring is relative to the quad, how well the core holds the trunk still over a planted leg. All of that responds to training, the same way a passing pattern does. It takes quality reps and it takes quantity of reps, done again and again until the movement is permanent. That is squarely our job.
Who I keep an eye on
Some players carry more risk and it helps to know who. Female players tear the ACL several times more often than male players at the same level, and a big part of that difference is in trainable movement patterns — which, honestly, makes a prevention programme matter most, not least, for girls teams. Then there is the player coming back from a previous knee injury, and the player whose mechanics fall apart when they are tired. That last one is the clue that load matters too. The FIFA 11+ is the evidence-based starting point for all of it, and the rest of this collection works through how to run it.