That's not what I said...
There's nothing that says someone MUST be charged. Only that the charges exist. Self defense is a legal defense of justification; the defendant is saying, in essence, that yes I did break the law -- but I had a good reason and shouldn't be criminally liable for my actions. Necessity is another defense of justification; the defendant wouldn't have broken the law but for urgent necessity -- like if you were in the wilderness somewhere and broke into a cabin on private property to stay warm when the temperatures fell below zero.
Thanks you beat me to it. Everyone tends to forget that self-defense is a legal concept excusing the reason you did what you did. It still can mean that you are charged and it is up to the judge/jury to interpret your actions as justifiable or not.
In Michigan here are the jury instructions to decide a case of self-defense. Read through them and see how you would decide based on what you now of the case and not what you THINK it should be. (Taken directly from Steffel on Michigan Criminal Law and Police Procedures, 2007 pg. 21, also noted that I did not include he/she pronouns since it is a male in this case)
1) The defendant claims that he acted in a lawful self-defense. A person has the right to defend himself under certain circumstances. If a person acts in lawful self-defense, his actions are justified and he is not guilty of (stated crime).
2) You should consider all the evidence and use the following rules to decide whether the defendant acted in a lawful self-defense. Remember to judge the defandant's conduct according to how the circumstances appeared to him at the time he acted.
3) First, when he acted, the defendant must have HONESTLY and REASONABLY believed that he had to use force to protect himself. If his belief was honest and reasonable, he could act at once to defend himself, even if it turns out later that he was wrong about how much danger he was in.
4) Second, a person is only justified in using the degree of force that seems necessary at the time to protect himself from danger. The defendant must have used the kind of force that was appropriate to the attack made and the circumstances as he saw them. When you decide whether the force used was what seemed necessary, you should consider whether the defendant knew about any other ways of protecting himself, but you may also consider how the excitement of the moment affected the choice the defendant made.
5) Third, the right to defend oneself only lasts as long as it seems necessary for the purpose of protection.
6) Fourth, the person claiming self-defense must not have acted wrongfully and brought on the assault. [However, if the defendant only used words, that does not prevent him from claiming self-defense if he was attacked]
IMO the reason this is being charged is there is enough doubt as to whether his actions for justifiable or not in the circumstances as they are known. You have a case where two people are escalating an argument and the 20 year old never made any attempt to leave (Duty to Retreat). Also, if it was an irrate customer, this should be handled by the manager and not the employee getting into an argument back and forth until it escalated into violence. Also, consider the jury instructions say that
appropriate force was used. An old man swings and misses and you hit him as hard as you can to knock him out will leave doubt into many jurists minds if that was appropriate to protect yourself.
Self-defense does not offer a blanket protection for people. It isn't a protection to get into an argument and escalate it and then pull the "well he swung first" card when there were times when you could have left safely or got intervention before it happened. I have spoken with prosecutors in our county and this would be viewed as a mutual combat issue, not a criminal assault so a S-D excuse wouldn't work and it would be charged and sent to a judge/jury (not this particular case, but most fights in general that start with back and forth exchanges). Their view of S-D is when someone starts trouble and you attempt to walk away and they prohibit you from leaving and/or attempt to assault you as you are trying to leave).