Revealing mistake: After Steelleg's and Iron Head's song, Steelleg is taken outside for a fight with some thugs. He kicks a ball into the stomach of a guy, making him fly backwards and roll over several times before he slides away on the ground. Look at his neck in the shot from behind - you can see the construction he was dragged by under the shirt.
Revealing mistake: In the opening scene Vinnie Jones is driving the red Mercedes CLK convertible. As the scene switches views of him driving, the view of Vinnie and the car changes in a flipped shot.
Revealing mistake: When Ali is in the rain on the pay phone at the motel it is a modern phone, not from the era they were trying to portray.