Continuity mistake: When Martha Johnstone falls on Justin during the cheerleading tryouts, her skirt falls up and is laying on her back; they show this in a front view; but when they switch to a side view, her skirt is back down covering her bottom. (00:06:35)
Continuity mistake: When Boobie gets in the car after clearing out his locker the car window is very dirty and spotted, but a few seconds later the camera shows the window again and it is perfectly clean and spotless. (01:11:45)
Continuity mistake: When Marni writes "BETTER" on the whiteboard, the handwriting changes between shots.
Continuity mistake: The fan who came out onto the ice and draped a flag around Jim Craig's shoulders (a cameo by the film's director, by the way) put it on upside-down. The camera cuts away, then cuts back, and it's suddenly right-side up.
Continuity mistake: In a couple of close up head shots of Paul Bettany in the final match, the tag in his shirt is visible. In one shot the size of the t-shirt is L (large), in a later shot within the same scene it says M (medium).
Continuity mistake: When Maggie is first shown in her hospital bed, you see her left eye is closed and swollen from the fight. Then, you see her left eye normal, then it goes back to swollen and shut. (01:33:20)