You were bullied often as a child, and you are now constantly ready to defend yourself with your fists when an enemy comes near.
Note that this trait does not grant the ability to make attacks of opportunity with your unarmed strikes—you must have a level in monk, the Improved Unarmed Strike feat, or some other similar power to gain the use of this character trait. However, that doesn’t prevent you from selecting this trait. You simply cannot make use of it until a later point if you do.
Pathfinder Roleplaying Game: Ultimate Campaign. © 2013, Paizo Publishing, LLC; Authors: Jesse Benner, Benjamin Bruck, Jason Bulmahn, Ryan Costello, Adam Daigle, Matt Goetz, Tim Hitchcock, James Jacobs, Ryan Macklin, Colin McComb, Jason Nelson, Richard Pett, Stephen Radney-MacFarland, Patrick Renie, Sean K Reynolds, F. Wesley Schneider, James L. Sutter, Russ Taylor, and Stephen Townshend.