Drumline

Nick Cannon plays a talented drummer(snare) who is recruited to college. He impresses the Band Director with his talent, and is offered an opportunity to play with a band that has been finishing 2nd in a National competition. Since a large part of a successful outcome depends on the quality of the drum section, the director feels that he may be the "missing key" to land them the 1st place trophy. The band director is under a lot of pressure from the schools administrator to win the National competition this year - the implication being that he is out if he doesn't.Canon's character Devon is a bold, brash young man and immediately causes tension with the Section Leader. Although Devon isn't given a starting position in the band, he feels that he deserves it. Additional tension ensues as Devon is constantly challenging and attempting to
show up or embarress the leader.Devon learns that he may be able to make it onto the starting squad by issuing a challenge, and then winning in a one on one challenge. There's just one hitch - Devon doesn't read music. He's managed to compensate so far by utilizing a near photographic memory and combining that with his almost savant talent to get by. He quite often just riffs, or plays combinations of drum sequences that he has memorized over time.There is a small sub-plot where the director of the number one band attempts to "bribe" Devon to switch schools and come play for him.Additionally there is a little time devoted to a romance angle that doesn't affect the story line.Devon finally demonstrates to the section leader that he is worthy of "starting" while additionally earning the leaders respect.The day of the big National competition arrives. Devon has committed an infraction that prevents him from starting. After all the bands have competed there is an announcement that there is a tie - you guessed it - between the number one band(that attempted to recruit Devon) and Devon's school. A "drum-off' is announced. The drum sections from each band will meet on the field and compete one at a time directly against each other.The band director asks Devon if he would like to see what it would be like to play on the field next year - then tells Devon to suit-up and go out and play in the drum-off.
The two competing drum lines tradeoff playing times and for their last performance the number one band marches literally right into Devon and his drum line's face and plays on their drums in addition to their own - ending with tossing their drum sticks right at Devon's drum line.
Devon's section responds in kind - even to the point of dropping their sticks on the drums of the number one band....then from out of nowhere they all pull out additional sticks and complete an additonal -"in your face" drum ending.After the two performances, tension ensues and the director makes use of all his cameras by showing the anticipation of all the participants and their supporters. The number one director is strutting and telling his staff that they won, when the annoucement is made that Devon's band won.The end credits include both some repeat scenes and some addtional cut scenes - some humourous - the others of the drumming.

Question: What prevents Devon from"starting"?
Answer: He  has committed an infraction.