When to use force
The use of force must be reasonable under the circumstances. Generally, force is reasonable when an offensive attack is imminent. One does not have to wait until an assailant strikes or even attempts to strike. Once the assailant demonstrates a clear intent to attack, coupled with an overt physical threat, one may defend. For example, if a person threatens to punch and cocks his/her fist to carry out the threat, you may begin your defense.
Amount of force
Most legal problems involve the amount of force used during a defense. The amount of force must be reasonable under the circumstances. Courts will consider what a reasonable and prudent person might have done under the same or similar circumstances. This means that a person's fear, confusion, and excitement will be considered to the degree that such emotions may reasonably be expected to influence ones behavior.
What is reasonable force
The issue of what is reasonable is often difficult for the courts to decide. What is reasonable in one circumstance may be unreasonable under another circumstance. Therefore, most states delineate certain circumstances when deadly force may be reasonable, such as when the attack is aggravated by the use of a deadly weapon or by multiple assailants. When one is in fear of losing his/her life or sustaining serious bodily injury, the courts may judge killing the assailant as reasonable force. In circumstances where the attack is only a misdemeanor attack, the law does not permit a person to use deadly force or seriously injure the assailant.