So I'm playing "Bully" on my PS2 (I know I'm 5 years behind on technology).

Suddenly my skateboard is accelerating without me pressing any buttons, and the world around me stops rendering, until I'm floating in a grey void. Then the game freezes.

I try again, and this time my character falls through the solid floor and dies. A third time I try, and when I go to the load screen the game freezes agani.

The other games I own for the PS2 seem to work, but the "Bully" disc doesn't seem to be damaged.

Any ideas what woudl cause such madness?