How do you cannon ball on Skate 3?

To perform a cannonball in Skate 3, start by gaining some speed on your skateboard. As you approach the edge of a ramp or a jump, press the grab button (usually the left bumper on consoles) to initiate a grab. While in the air, pull the left stick down to crouch your character, simulating the cannonball position. Release the grab button just before landing to complete the trick.