In Tony Hawk's Pro Skater, Tony Hawk's special trick is The 900. The move is named for a 900-degree rotation—two and a half turns—performed in the air on a vert ramp, and it became closely associated with Hawk's career and the video-game series.
Hawk famously landed the first documented skateboarding 900 at the 1999 X Games in San Francisco after repeated attempts. The achievement was a landmark moment for vertical skateboarding and helped make Hawk a household name just as his video-game franchise was launching.
The other choices are standard skateboarding maneuvers or rotation terms, but they are not Hawk's signature special move in the game. The number refers to the degrees of rotation, not a level, score, or button combination. The 900 also appears as a major part of Hawk's broader public identity, beyond the game itself.