You naturally move close to your opponents when fighting, instinctively grabbing and punching rather than striking with weapons.
You gain a +1 bonus on unarmed attack rolls and grapple checks.
You take a -1 penalty on all other attack rolls.
The bonus from this trait doesn't apply to natural weapons. A character with the Improved Unarmed Strike feat can't select this trait (if a character with this trait later gains that feat, he loses the trait).
Characters with this trait often disdain the use of weapons entirely, and some eventually learn more refined martial arts based on their instinctive fighting techniques. Many brawlers might not even be consciously aware that they fight differently from other characters; they simply know that the best way to take someone out of a fight is to grab him or punch him in the face.