Like its predecessors in the Tony Hawk's series, Underground is centered on skateboarding in a series of levels.[2] The player performs tricks via combinations of analog stick and button inputs. For example, the player initiates an ollie (a jump trick) by holding and releasing the jump button. During an ollie, the player may change the position of the analog stick and press one of two buttons to perform either a flip trick (such as an impossible or kickflip) or a grab trick (such as a benihana or nosegrab). The player can grind on certain edges and rails; different tricks may be performed during a grind based on the position of the analog stick. On quarter pipes, the player may execute lip tricks. While skating on flat surfaces, the player may manual in multiple ways via button combinations. Miscellaneous tricks include acid drops and wall-rides.[3]
While a grind, lip, or manual trick is underway, a balance meter appears: unless the player prevents this meter from falling to the left or right, the character will bail and need a few seconds to recover. Bailing can also be caused by falling without one's board facing downward. Completing tricks in succession without bailing is called a combo.[3] Comboing raises the player's score and fills up the Special Meter; when it is full, the player is granted access to more elaborate tricks worth more points, such as the McTwist and 540 Flip.[4] Underground introduces the ability to dismount one's skateboard, which allows the player to explore levels more carefully and reach new areas. Each level features at least one vehicle, usually a car, that the player can drive.[2]