There are many factors to be considered when the use of self defense is used.  Many states differ with their opinion on what they consider valid self defense. These things include the extent, who it is used on, who is using it, and the reason why.

The act of self defense is the use of force to defend one's person from an attacker or a threatening situation.  The force must be reasonable.  Self defense is in place to protect you from being convicted of a crime if you afflict harm on the person who is attacking you.  A good example of self defense is if you had a struggle with a robber and ended up using the robber's weapon against him.  You will not be responsible for causing harm to the criminal.

Some states vary what they consider self defense.  You may have a can of pepper spray in your purse for personal protection.  If you are approached by an attacker in the parking lot of a store and about to be car jacked then the use of your pepper spray would be appropriate and could ultimately save your life.  Some laws in certain states would say that the use of the pepper spray would be inappropriate and illegal.

The extent is a big factor when self defense is considered.  How far is it that you had to go to defend yourself against the attacker?  When you use self defense and you have a gun you might shoot the attacker.  When the extent is taken too far , such as when you continue shooting into the attacker when all you had to do was disable the person so you could get away.

Who you use the self defense on is another factor that has to be considered. You may think you are defending yourself if someone puts their hands on you but the person is a factor.  For example, when you are thrown out of a nightclub by a few bouncers you do not have the right to physically defend yourself with pepper spray, tasers, stun guns, or anything else.  You are not allowed to use physical force against police officers and any official that is restraining you for any reason.  This could land you in jail.

The reason why self defense is being used is a big factor.  If you have personal protection devices that you carry on you for safety and you are in a situation where you feel unsafe you can use them.  Circumstances such as where you are walking down the sidewalk late at night and you are approached by a person demanding you to come with them then you have the right to protect yourself.

There are many factors that the government will consider when they look at cases of self defense.  Know the laws in your state.  Know which personal protection devices you can use and to what extent you can use them.  You don't want to go to jail for fighting off a rapist.  It has happened in the past.