When leaving the fair Frankie has a Toffee apple then in the next shot it is a half eaten giant cookie.
When Axl drives onto the demolition derby field you can see the right side of the car has already been damaged as the mirror and door are smashed in. This was apparently the 2nd take of the scene.
There is absolutely no possibility that the man with the flag would have thought Axl's car was supposed to enter the demolition derby nor would he have allowed it to enter the arena if he tried. Anyone associated with demolition derby's is well aware that ALL GLASS - including windshields, windows and mirrors - must be removed before a car can enter.