Why does a dog go after one person and not others?

Could be the way the person smells, could be whether the dog detects fear or perceives one person to be an easier target.

There could be a variety of reasons, they can go after the mailman because he comes onto your property. You see it as mail delivery, the dog sees them as a trespasser

Dogs have personalities just like people, do you like everyone you meet?

When I was young, I was playing a game of baseball for my team. I was in left field when all of a sudden out of nowhere, this dog came and chased me. I was running and it was very embarrassing. Then, it bit me and I slammed my fist into it’s head and it ran away probably in vertigo. I have hated dogs ever since.

ha 90s kid you got pwned.

I’m guessing because a dog can only go in one direction at a time.

@kid: Yeah, that’s not vertigo.

What do you mean by, “go after”? Attack? Go say hello to?

Dogs are masters of body language (they have to be, to be able to survive in a pack). They pick up on any number of cues that we may not recognize. An aggressive (alpha) dog may attack a person who has strong eye contact because it’s a challenge. A lower status dog may attack someone who appears fearful in a effort to establish dominance over that person. They may being protecting territory or may have developed a negative association for some detail in the past (someone in a hat, someone carrying a stick, etc). There are too many variables to be able to answer your question.

If you have an animal that is showing aggressive behavior to certain individuals, you need to find a highly qualified dog trainer (preferably someone with a degree in behavior) and get him signed up for training. In today’s litigiousness atmosphere, you do not want to own a dog that is a time bomb for an attack.

Patterns I’ve noticed (also already mentioned):
They can be defensive of some newcomers to the property that they are settled on.
They’re like an detector for the human companion or other dogs that also exist on “the property”. Other group animals are also like that.
I’ve seen what Sys sees where a high status or low status individual will challenge “threats” too their status. (Seems we do that too, eh?)

And also whenever they detect someone acting in a way that makes them feel uncomfortable. I wish I were a dog now, so that I could enumerate the ways.
certain eye contact
erratic motion
“suspicious intention”? (the can detect this well).
How well can they detect low self confidence or fear? Hmm.. body language. :)

I was 8!! (or around that age)

Not when you wrote that.