The Macasini was named after the two men who invented the trick: David McDonald and Billy Rosini. It is a front somersault while moving backward and is actually easier than it looks.
The key is to have plenty of speed at the wake. Just before approaching the curl of the wake, perform a 180 counter-clockwise if you're heading to the right and clockwise if you're heading to the left. Resist the wake and as you come off of it, throw your head straight down to your knees and let go of the rope with your outside hand. Hold this position until you land. As you gain more experience, you'll be able to straighten up your back more just before the landing.
A word of caution: You must be fully committed to performing this trick. Any attempt to bail out in the middle of the trick could result in a very painful mistake.
I can't get fully around. You may be throwing the trick too soon or you're not throwing your head toward your knees hard enough.
I come out of my board as soon as I throw the trick. You're throwing it too soon. Wait until you're in the air.