When in doubt, look at The Outsiders. You got stabbings and shootings and it's handed out to high school kids like it's candy.
As dragonkid pointed out, it's in the delivery and purpose. My own YA WiP has an attempted rape, a beating, and a grisly death. I may not describe the blood and carnage in quite the same way I would if I were writing an adult horror novel, but it's in there.