Going by the Book (2007)

A string of bank robberies sets off a public panic. To appease the residents of the city and fulfill his own ambitions, the newly-appointed chief of police decides to hold an anti-bank robbery drill to demonstrate the effectiveness of the police.

He secretly appoints a naïve traffic cop to disguise as a robber, overlooking the fact that the inflexible, by-the-book officer will go all out in accomplishing any assigned mission even when it's a robbery.