Close Quarter Combat
The best form of self defense is close quarter combat. The biggest problem with over 99 % of self defense that is tault to civilians. Is the simple fact that it is designed for law abiding citizens to defend themselves from unlaw abiding people. By using non lethal methods.
For example A is the attacker and D is the person who is defending themselves and C is a British police officer.
A is a crinimal who has likekly had a lot of experience in violent confrontations.
A is not concerned if their methods are illegal or if they permanently maim or kill the victim.
A has nothing to loose they are not concerned if they are arrested or punished for breaking the law.
D has been trained in legal methods of self defense and probably does not have much experience in violent confrontations.
D does not want to be arrested or pushed for breaking the law. D does not want to permanently injure or kill his attacker/s
C does have experience in violent confrontations and has been trained in legal methods of self defense. However C must consider all of his actions and the possible legal consequences. C must be prepared to to justify their actions in a court of law.
Instantly in any situation D has a huge disadvantage and his legal methods may or may not work. I would estimate that D has a 30 % chance of defeating A.
C also has a disavange over A as C must not break the law when arresting or defending themselves or others from A.
In any self defence situations you should have only 4 rules.
1. Defend yourself by any means possible even if it is not legal.
2. Have zero considerations of the legal implications of your actions.
3. Kill or be killed, maim or be maimed.

4. Avoid the Police 🚔 if you have used lethal methods or caused serious injuries.
I have been involved in many violent confrontations from a young age in many different countries and have resorted to less than legal methods to defend myself. I have talked my way out of violent situations and I have also run 🏃♂️ away from them. On a few occasions I was not so lucky and was badly beaten.
Why is Close Quarter Combat so effective
Close Quarter Combat was designed to be a brutal and effective as possible. It is easy to learn and retain unlike traditional martial arts. CQC is used in life and death situations. It was never meant to be used by civilians as a means of self defense. The very fact that it was not designed for law abiding civilians is why it is so effective.
Where can I learn it ?
That might be more challenging as it is not generally tault to civilians. I was fortunate to have been able to train CQC with former special forces personal but, they are not currently teaching it. Depending on where you are in the world you may be able to find a former CQC instructor. Failing that some videos on YouTube could help you become familiar with some techniques. Some books are available and a good one is " United States Marine Corps Close - Quarter Combat Manual " but, in reality you do need a good instructor to be able to effectively learn it. Another option would be to join a Krav Maga class although it is tonned down significantly it is still a good option.
The best option
A large proportion of violent confrontations can be avoided by not putting yourself at risk in the first place. Situational awareness and avoidance is always the best way to prevent a situation becoming violent. It is always best to walk or run away to avoid certain situations that could become violent. Only resort to violence if you can not get away or if you can not avoid it by other means. But, if you have no other option other than to use violence then use as much brutality as possible and do not stop until the danger has passed. That might mean striking an attacker when they are on the floor until they no longer pose a threat.