The Boomerang, a pole dance spin, is also known as the Carousel Straddle, Open Leg or Open 'V' spin. The key to this spin is holding yourself away from the pole to spin.
Use your dominant arm to hold the pole on top and grab the pole on bottom like you are taking change from a cashier. This is the arm that is going to hold your body weight away from the pole as you spin. Also, keep your legs straight out and toes pointed to lengthen the legs as you spin.
Here is a video clip that demonstrated the spin: