To do the Roast Beef grab, launch yourself (safely) off of a fairly large kicker keeping your trajectory straight and forward. After you have taken off of the lip of the jump keep your board parallel to the hill and bring your knees and board up to arms reach. Bring your rear hand down and reach between your legs to the heel edge of your board trying to get as close to your back foot as possible. Keep your front hand up for direction and balance. Hold onto the grab for as long as possible. You can tweak this as much or little as your style allows for .. Roast Beef Air or Roast Beef Shifty.
Once you got the Roast Beef Air try a FS1 Roast Beef (Front side 180 Roast Beef Grab). Keep bigging it up!
If my description wasn’t clear enough, check out this awesome link I found on You Tube.
*Photo credit to someone who blogs, many thanks.