This is a complicated trick and is difficult to perform, but very impressive and surprising. You need a heavy flyer and a relatively light safety line operator. The flyer performs a bridge with the catcher (in safety lines). While they are locked in position, the safety line guy pulls as much as he can on the safety line rope and gets a good grip as high up as he can. On a predecided signal, the flyer lets go of everything and drops straight down. The catcher swings away. Meanwhile then safety line guy does not lose his grip on the lines and shoots up in the air as the heavy flyer falls. Having positioned himself so that he does not take a mouthful of the underside of the net on the way up, the safety line guy swings up towards the catcher on his rope (Tarzan style) and catches the catcher as he swings back.

These notes are provided ONLY as an explanation of the trick.
If you want to perform it yourself - get an expert to teach you.