This trick is a popular catcher dismount that can also be performed by flyers. For more info, see the corresponding Trick in the 'Catcher Dismounts' section (Trick ID 144).
Swing out and turn around on the bar. Get up into a sitting position. As you approach the frontend, drive your legs forwards to generate rotation and roll backwards off the bar down onto your back in the net.
The trick can be performed tucked, piked or straight, and with one, two and even three somersaults.
You can find out more about this trick in my books:
Thanks to Maybel for providing a video for this page.