i assume he fell knees-first in a way that he wasn't expecting so much of the weight of the defender(s) on his backside. The femur head ripped out of the joint through the rear. So if you were standing, the femur would be jammed up into the hip, but since his legs were oriented how they are when you're sitting in a chair, it sheared out behind.
There's been comparisons to Bo Jackson, obviously, which would have been okay (if I understand correctly), except that they (or he) popped it back into the joint soon after. Now, they have the sense enough to diagnose before they'd do something like that. The severed vein/artery in Jackson was just left to bleed out into his body for a time.
The medical staff was probably just limited to their era, and Dr. James Andrews surmised Jackson dislocated it because of the extraordinary force he created while running. That's all true, I'm sure, but so, too, was Jackson's reputation and toughness. He knew something was very wrong/different/unique with his injury, and didn't make it clearly known. The medical staff, as competent as they could be, still saw Jackson as a super man, as we all did.
Tua will be carefully diagnosed, studied, and fixed.
