The uniform numbers in American football are unusual compared to those in any other sport. They are displayed in more locations on the uniform than in those of other sports (on both the front and back of the jersey, on both shoulders, and often on the helmet), and they are very large, taking up almost the entire front of the jersey. More importantly, certain numbers may only be worn by players playing particular positions; thus the jersey numbers assist the officials in determining possible rules infractions by players.