The name in this case pretty accurately describes this move. Horizontal split also exists, but is harder.
You can start this move from seated. Let’s say you want to do splits with the left leg in front (because that happens to be my more flexible side…). Similar to how you would get into hocks on the top bar, invert, but instead of piking through with both legs, put one on each side of your righ arm. Your hands should be holding on to the top bar. Hook your left knee over the top bar just left of the attachment so that you are most balanced. At the same time, slide your right leg down the side of the hoop, keeping it “behind” the hoop, on the same side as your body. Once your legs are vertical, extend the top leg into a split. Lean and arch your back to look pretty.
You can exit in the reverse of how you came in, or by doing hocks on top and sliding to the side of the hoop into cradle.
A good demonstration of the move can be found on Circus Dictionary.