the thing that is catching your chain when you roll the bike backwards is your front derailleur.

your derailleurs are the things that derail the chain from one gear onto another.

it's not much to worry about.

as far as being able to reverse a bike... the best way is to get off of the bike!

bikes aren't designed to ride backwards because it would be almost impossible to balance. bicycle balance only works well when the wheel that steers is the one that's in front, and if you were going backwards the wheel that can turn would be actings as the rear wheel. riding a bike backwards would be a little bit like trying to drive a truck, at highway speeds, in reverse, with a trailer attached.