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 Missouri, assault is defined under Missouri Revised Statutes, Chapter 565. Assault in Missouri is categorized into different degrees, with varying levels of severity and corresponding penalties. First-degree assault, the most serious form, involves attempting to kill or knowingly causing or attempting to cause serious physical injury to another person. Second-degree assault includes attempts to cause serious physical injury or physical injury by means of a deadly weapon or dangerous instrument. Third-degree assault encompasses knowingly causing physical injury to another person, or recklessly engaging in conduct which creates a grave risk of death or serious physical injury. Additionally, Missouri law recognizes a special category of assault against law enforcement officers, emergency personnel, or other protected officials. Assaulting a law enforcement officer or peace officer while they are performing their official duties can result in more severe charges, often classified as a higher degree of assault or with enhanced penalties. The exact charges and penalties can vary based on the circumstances of the incident, the degree of injury caused, and the specific role of the victim.