Next in the series of "FAR"s or Frequently Accessed Rants...
When someone says "I have green pustulent tentacles sprouting from my back and a vaginal discharge the color and consistency of Steak Diane. What should I do?" the only correct answer is "See a doctor."
When someone says "I want to stay on the right side of the law, but I don't know exactly what the law is. What should I do?" the only correct answer is "See a lawyer". If you really want to learn a lot about it also take Massad Ayoob's LFI-1 Judicious Use of Deadly Force.
It doesn't cost that much to see an attorney. If he or she doesn't have the answers immediately at hand the research is just a trip to the bookshelf away. The lawyer will be able to translate the legalese and look dig up the relevant case law on the subject.
So, SEE AN ATTORNEY.
I'm only going to qoute one post -- because it's got the most important advice.
If you need legal advice & guidance -- you need an attorney, not well meaning friends (unless they happen to have passed the bar AND be experienced in the area of law you need help with), not martial arts practitioners with good intentions, or even internet "experts" who
know what they're saying. You need the best lawyer that you can find funds to hire, even if you have to beg or borrow to do so.
That said -- I'm not providing legal advice, nor am I an attorney of any sort. If you want specific legal advice... see above. I will share my opinion based on my training and experience -- which may not hold water any where else, but can be used, with at least $3, to get an overpriced cup of coffee at Starbucks or any similar chain.
Broadly and generally speaking, it's important to remember that self defense is a claim of justification. You've admitted that you've done something that would, ordinarily, be wrong. You've hit someone without their consent or permission, and probably with the intent to do them harm. That's battery, simple or aggravated assault, or whatever the law in your area calls it. BUT, you're saying, you had a really good reason -- namely, you though that the guy was going to hit or hurt you or that he already had done so. The law says that we don't have to let others hurt us; we can use force to protect ourselves from harm. But the law also says that the force used has to be reasonable and appropriate to the threat. The reasonableness is judged in the light of both you, and the guy who was posing the threat. Factors include weapons used/presented, relative fitness and exhaustion, age & infirmities, whether you tried to retreat/avoid the situation, and lots more. Bottom line -- this is a complicated issue. You can generally respond with similar force, or even slightly higher, than is used against you -- but only slightly. You can't shoot someone because they pushed you. You can't use a physical technique that you would reasonably know is likely to cause death/serious physical injury unless the person is presenting a similar threat to you. I'm not even going to try to lay out examples here; it's just too complicated. A lot depends on how you explain yourself; a lawyer will help you do this the right way. One thing that a private citizen almost never can do is resume the attack after the original assailant has tried to surrender, flee or simply given up the attack. And -- lethal force (that is, force likely to cause serious bodily harm or death) is almost never justified to defend mere property. (Exceptions include defending certain military equipment, like nukes. The nice Marine tells you get back... Get back FAST.)
If you do find yourself forced to use force to defend yourself (sorry; couldn't resist the pun), as soon as you're safe -- call the cops. Ideally, don't leave the scene unless it's necessary to do so for your safety. Advise them of any injuries to yourself or your assailant. If you have the training, and can do so safely, it would probably look very good if you attempted to render aid to the guy you just took down. A lawyer will tell you not to speak to the police; personally, if you're pretty confident that you did nothing wrong, I'd say give the basic facts to the officers. Otherwise, they're liable to look at injuries, and arrest you when a brief statement of the facts might have avoided that situation... Don't lie, whatever you do. Whether you want to volunteer martial arts training is another difficult question; don't lie, whatever you say, because if I or another cop catch you in one lie -- we're going to assume there are more. Don't be surprised if you are cuffed, at least initially, until the situation is straightened out. And -- if you are arrested -- go with the program. Don't argue, yell, complain, or anything else. Just go along; the time to argue, complain, and so on is at court. If you are arrested -- get a lawyer. You don't know the playing field; you'd be unwise to go into court without someone who does.