A punch that takes someone by surprise, a punch coming from out of the blue.

A stupid person; it refers to the lack of surface area on an individual's brain. The general thought is that the more surface area (wrinkles, creases, etc.) a brain has, the smarter the person is. Conversely, a person with a smooth brain (no wrinkles) has less surface area and would therefore be stupid.

Easily confused with a punch defined as a "bitch move" a true sucker punch is quite a bit more complex than a simple unanounced attack.
It primarily involves a closed fist contacting the soft underbelly of a person (beneath the rib cage) at a high velocity, causing the ensuing force to press upward on the victim's diaphram, leading to a sudden expulsion of air from the victim's mouth and lungs. This opening blow leaves the victim open to various other attacks, often leading to what would be called "bitch moves" becuase of the defenseless nature of the victim.

When someone punches you and you didn't evan know you were fighting

This occurs when someone hits someone else from behind, usually when the person being hit doesn't know it until afterwards. Usually considered shady or a "bitch move".

A punch that takes your enemy by suprise, possibly knocking them out.

Comes from them being a sucker for not having their guard up

What Floyd Mayweather did to Ortiz on September 17 2011..