OK, good info. I always thought it was side-to-side since that's how I blew mine- I was hit while my foot was planted from the side- in the thigh. I was also told to avoid cutting movements like those in basketball and soccer.
It's very common to shred it with a combo of sideways +/- a little forward force on the leg. Angled torsion will also do it. Twisting injuries are quite common. Animals most often injure it while either jumping (and landing wrong), or when they run into something or something (usually another animal) runs into their leg at the wrong moment.
The side to side cutting motion is what continues to shred the meniscus after the ACL is gone. There are actually 2 points of attachment of the top part of the ACL which is where it usually shreds (in animals, anyway). One part does a little more lateral/twisting control. Animals can have partial tears of just the part that does the angled control (and I believe people can, also).
Animals with a partial tear will carry the leg some, but will put it down some, too. It hurts, but they can still walk pretty well. I find it when I manipulate the knee when flexed, but it will still be pretty solid when manipulated straight. If there is a complete tear, they will usually carry the leg completely unless their other leg has severe arthritis and they can't carry the freshly injured leg.
Animals (and people, too) often get collateral ligament damage along with ACL damage. It is rare for animals to get ONLY ACL damage without at least some collateral damage. They can get meniscal tears along with ACL damage, but not quite as often as collateral damage. I don't know what the actual odds are in people, for collateral vs. meniscal damage, but I do know that people pretty often get at least a little meniscal damage and would guess that they even more often get collateral damage similar to animals.
Anyway, the recovery time for surgery is usually quick enough for most athletes, that you could potentially be back to riding if you get that surgery done ASAP. If you don't, and you cause more damage by continuing to walk on it and/or ride, you could potentially never ski again. Certainly would likely never walk again without pain. Once your cartilage goes, you are on a never-ending slide into joint deterioration and arthritis. Your choice.