A legs catch is possible when the flyer finishes their trick facing upwards with their feet towards the catcher. The flyer puts his feet behind the catcher's shoulders, and the catcher reaches over their head and grabs behind the flyer's legs. The flyer swings with the catcher hanging upside down.
Examples of tricks that use this type of catch are a basic Legs Catch, and also any back somersault with a half extra somersault at the end (One and a half, Two and a half etc.)
You can find out more about this trick in my books:
Thanks to the team at Circus Arts Australia and Fly'n Fit Trapeze School in Japan for providing videos for this page.
IMAGE CREDIT: 1st: Reno, Diana. 2nd: Emerald City Trapeze Arts, Heather and David Treadwell