The crime of assault varies from state to state (and under federal law), but is generally defined as intentionally putting another person in reasonable apprehension or fear of an imminent (immediate) harmful or offensive contact. The crime of assault may be committed even if there is no physical contact, as the criminal physical contact constitutes the separate crime of battery. In many states assaulting a police officer or peace officer who is performing official duties (such as making a lawful arrest) is a more serious offense—sometimes a felony.

In Iowa, assault is defined under Iowa Code section 708.1 as any act which is intended to cause pain or injury to, or which is intended to result in physical contact which will be insulting or offensive to another, coupled with the apparent ability to execute the act, or any act which is intended to place another in fear of immediate physical contact which will be painful, injurious, insulting, or offensive. Additionally, the act must be done without the other person's consent. Assault in Iowa can be classified as a simple misdemeanor, serious misdemeanor, aggravated misdemeanor, or a felony, depending on the circumstances and severity of the act. Assaulting a police officer or other peace officer is considered an aggravated misdemeanor under Iowa Code section 708.3A, and can be elevated to a felony if the assault causes serious injury or is committed with a dangerous weapon. The specific classification and penalties can vary, with more severe consequences for assaults against protected classes of individuals, such as police officers, and in situations where the intent to inflict serious injury or use of a weapon is present.