A Reverse Bar catch is used when the flyer finishes their trick facing upwards on a Bar-to-Bar rig. It is therefore identical to a Stick catch, except that instead of grabbing a Stick held by the catcher, the flyer grabs another fly bar.
Examples of tricks that use this type of catch are: Reverse Knee Hang, all Reverse Position tricks, Cutaways with whole numbers of twists (zero, full etc)