Being able to understand your enemy and to know what he knows, would you be able to defeat him? Would you use it against him? All the generals in the human history were trying to get that information about their enemies and build their tactics on it.
People kill each other for information and today, information is the most expensive commodity.
When you deal with a criminal in a street fight situation, it is the same.
If you understand his intentions, find the engine that makes him do what he does; get to his emotions and lure them out to your advantage, all this will help you make your fight with him more effective and even give you a clue about how to defeat him.
Here is how a criminal chooses his prey:

• his victim seems weaker than him
• the victim is not likely to fight back
• criminal counts on fear factor so the more mentally imbalanced you look, the more likely you will be chosen as a victim

What a criminal doesn't want to happen:

• he doesn't want to fight - he wants to make everything as fast as possible so he won't be caught
• he doesn't want to be seen, recognized or hurt
• a criminal doesn't to draw attention on him

What you should do when dealing with a criminal:

• if you think your opponent looks like a worse runner - RUN!
• if you are not directly endangered with weapon, try to draw attention to you
• make the act as long as possible - fight for time (talk to the criminal, play ham-handed..
  )
• act strong and healthy, use strong voice and don't show your weak spots
• if you are fighting him, try to leave a visible sign on him - scratch, bite, anything that will help to catch him
• use your environment - things can be used as blunt weapons, find places to hide or use obstacles when running

Criminals are always trying to get what they want as quickly as possible and if someone interrupts them or make the act longer, it makes them nervous.
Usually they run away, not finishing what they wanted to do or trying to get it by force...
that is when you start to fight and that is when you need to know something about street fight! Be ready for any situation that can occur.
Learn how to fight and use his feelings against him.
It can save your life.