Stunting is the collective term for the special moves: Flips, Dodges and Hops. Stunting is crucial if you want to get the most performance out of your toon’s vehicle. Also, all Smack Points earned while stunting are doubled.
You can perform a Flip by flicking up on the right stick. Your vehicle leap up and do a 360° forward roll and land on its wheels again. Forward flips give you some extra speed and earn you a boost on your boost meter. You should use flips whenever you have a stretch of clear ground in front of you to build up boost, and it can be very useful to jump over obstacles.
You can perform a Dodge by flicking left or right on your right stick (or by pressing L1/R1 on PS3 and PS4). Your vehicle will leap up and turn over sideways into a 360° barrel roll and land on its wheels again. Dodges make you less susceptible to damage for a moment, and can be very helpful in getting out of a tight spot. If you dodge onto an opponent you can flatten them momentarily; this can be useful in Gate Relay or when you are unarmed or to retaliate on a flanking opponent.
You can perform a Hop by flicking down on the right stick. Your vehicle will do a small vertical jump. Hops are helpful when you want to jump over a small gap or obstacle but don’t have the room for a full Flip.
Any time you are in the air, you can use the left stick to reorient your vehicle. Doing so will also slow or stop your rolling to help you land wheels-first. Note that in many cases your vehicle will land on its wheels without having to do anything; this just lets you finesse it.