Posterior cruciate ligament tears are usually caused by direct posterior blows to the knee.

“usually gets torn from a direct blow injury from falling on to the knee but falling specifically on the tibial tubercle and it's not easy to do that I mean most the time you're falling more on your patella but if you fall directly on your tibia you will drive the tibia backwards posteriorly and that's what puts the PCL on stretch and it gives out”