in bodybuilding/weightlifting you see and hear talk of how not to snap your stuff up. Lift this way to prevent injury. However one glance on YouTube at some Crossfit gyms and it's like WTF??? People yanking those deadlifts up with curved backs, throwing stuff around and yeah jerking and swinging on the pull-ups.
Crossfit is a good theory but I'm not sure there is sufficient training yet for the practice. The word "functional" gets thrown around so much it's become almost nonsensical. What function would say, a schoolteacher have, to warrant balancing on a bosu ball and overhead pressing even 100 lbs?
Like I said, I have nothing against the theory, it's cool, but currently it's a lot of functional ER visits in the making. If you are a Crossfit person, more power to you, but be safe and don't listen to anyone telling you to do anything you know may snap you up.