I have seen kids who have terrifying fears of going backwards. I think that all stems from not going backwards enough as a little one. From those frogs legs from fears of going backwards in back handsprings, to doing back flips, it all is from an original fear of going backwards.
I like to do a lot of drills of going backwards, especially small drills they can do by themselves. I start normally with just backing up walking backwards (I have them pretend like they are in a car of truck and make the beep beep beep beep noises as they back up). Walking backwards leads to jumping backwards, to hopping backwards, skipping backwards, crawling backwards, crab walks backwards, etc.