Continuity mistake: When the Horsemen team are ready to play the start to skate up to the arena. You see a back view and Jonathan clearly doesn't have his white T-Shirt over his black suit. They cut to someone else then back to the team and Jonathan clearly has his white shirt on.
Other mistake: In the scene after Jonathan and Aurora have sex in the gym, Jonathan gets on the company plane. You'll notice that he grows a massive beard overnight. Then, in the next scene, it's semi-shaved.
Visible crew/equipment: When Toba is skating simple-mindedly on one side of the track (before he gets hit), you can see the Rollerball fans are just cardboard cut-outs of people.
Continuity mistake: In the final game, Jonathan (Chris Klein) skates up and punches Halloran, the big guy that plays for the horde. Halloran turns and punches him twice, knocking Jonathan's helmet off. We then see another player stroll up and hit Jonathan in the back with a piece of gear, and his helmet is magicly back on.
Visible crew/equipment: When Jonathan throws the Rollerball into the glass of the Media room in the final game, if you look closely you can see he's wearing his red helmet, even though he lost it earlier.