It's all a matter of force, inertia, momentum and gravity.
People whose legs are strong enough can do a back flip in a layout position (without a tuck.)
The only thing a tuck does for you is allow you to rotate faster.
No you really dont have to be flexible. Im a gymnast and i have had a back tuck since i was 7. Sone of my friends are super inflexible and they still can do it. As long as you have strong legs can tuck into a ball and practice you will be able to do it
I think contributor Shan has the correct answer!
were you dropped on your head as a kid
