Assault can occur in a civil or criminal context (or both). What does this mean? Well, if assault is part of a criminal case it means the government is alleging assault against a defendant on behalf of the state. In contrast, in a civil case, a plaintiff would file a private civil claim of assault against a defendant (generally for money damages).

Assault is generally an intentional tort which occurs when an individual voluntarily places another individual in "reasonable apprehension of an imminent harmful or offensive contact." The actor must actually "intend" to act. In other words, an "accident" could not be an assault (but it could be negligence). And a "reasonable apprehension of imminent harmful or offensive contact" essentially means that the actor must place another person in "imminent" fear of being harmed. This means an assault cannot occur if the actor says he or she is going to harm another person in the future. The threat of harm must be immediate, not later. So, if Bill told Ted that he was going to hit him tomorrow that would not be an assault.

Further, if you look at the definition above, it starts off by saying "the threat (or use) of force." This is because the original definition of assault only included the threat of physical injury or harm to another person which placed that person in imminent apprehension of the harm. It did not include the actual use of force. So, a person would be found guilty of assault for merely threatening to injure someone where the other person felt he or she would immediately be injured.

In contrast, modern definitions of assault may include actual physical offensive or harmful contact with another. However, actual physical offensive or harmful contact with another is really the definition of battery. But many jurisdictions do not differentiate between assault and battery and in such jurisdictions any act of assault or battery is often just called an "assault."

Let’s go over a brief example to show how the definition of assault works.

Assume Greg was picking on Johnny on their walk home from school in front of all their friends. Johnny got real mad and picked up a rock and threw it at Greg with the intent of hitting Greg. Assume that Greg never sees the rock and it sails past Greg and goes into the bushes. Is Johnny liable for assault? Answer: No. Why? Because Greg was not put in immediate apprehension of harm because he never saw, heard, or knew the rock was headed at him.

Now, assume that Greg clearly sees the rock and it goes sailing past him. Here, Johnny would be liable for assault because Greg was put in imminent apprehension of being hit by the rock.

Now assume that Greg is actually hit by the rock, but Greg is not hurt by it. Johnny would still be liable for battery because the rock actually hit Greg, even if Greg was not hurt by the rock. But as stated above, in some jurisdictions, they would just call any assault or battery an "assault."

With all that said, different jurisdictions have different rules for both civil and criminal assault. The above example where Johnny threw the rock and Greg did not see it could still be an assault in certain jurisdictions. You’ll have to look into the rules in your particular jurisdiction.

There are also questions on what constitutes aggravated assault. In short, aggravated assault is a worse form of assault and generally means that the actor intends to do something very harmful to the victim (e.g. rape, murder, torture, etc.) or uses a deadly weapon to place the victim in fear. Once again, keep in mind that the legal definitions of "aggravated assault" very from jurisdiction to jurisdiction, and may be called different things.

Also, keep in mind that there are many kinds of defenses to assault, including consent, self-defense, defense of a third person, necessity, defense of property, etc. In other words, if a plaintiff files a claim of assault against a defendant, the defendant can argue that one of the defenses apply.