A hit and run refers to the act of causing or contributing to a car accident and then leaving the scene without stopping to identify oneself. It is illegal in every state to flee the scene of an accident without exchanging insurance information or, in a more serious accident, waiting for emergency personnel to arrive.
In all but three states, a hit in run is classified as a felony if a person is injured or killed as a result of the accident. In most states, hit and runs that result only in property damage are classified as misdemeanors. The policy behind making the hit and run a crime stems from the difficulties that early car accident victims faced in identifying wrongdoers. Aside from the obvious problem of a vehicle fleeing the scene quickly, early drivers typically wore driving goggles that, while protecting the driver's eyes, also hindered the driver's vision.
Most often, drivers will flee the scene of a car crash if they do not have insurance or if they are under the influence of drugs and/or alcohol.