The way I've personally thought would be best to describe it is a full rotation where your feet go over your head. Both feet need to leave on the same frame, as well as land on the same frame. The reason for the last two restrictions is to prevent weird gainer cheesing. Both feet leave the same turn, both feet land the same frame, and your feet must leave the ground, rotate backward and over your head, and then must touch the ground. When they touch, it needs to also be the same frame for both feet just like leaving. I think this could be explained in much more simple terms, probably, but it works for both front flips and back flips and shouldn't leave room for cheesing it with gainers or anything weird.

I wonder if for interest sake, the timing should start as soon as the replay starts? This wouldn't allow people to do interesting setups like pusga did, however it might prove to be more interesting as otherwise it will just be mostly about the setup. Not sure how I feel about this but figured I should mention it just in case.