A fight doesn't always start with two or more would be combatants standing face to face, with full knowledge that they're all about to throw down. Sure, that occurs when tensions rise through dialogue. A stand-up fight is the very foundation of a duel, showdown or an invitation to step outside. All participants realize that a physical struggle is about to commence, and all can react.
Other times, a fight gets started with at least one party caught by surprise. Someone arranges an ambush for a victim or enemies encounter one another by accident. Under those circumstances, only the quick and the alert react in time to act or defend themselves. When your character walks into an ambush or unexpectedly stumbles into an opponent, you must check to see if he can respond. Roll Perception+Alertness. If you get no successes your character is taken unawares and cannot act in the first turn of combat. Initiative is rolled for him in the next turn. One or more successes allow your character to behave normally and respond to the encounter.
Obviously, ambushing attackers get to act normally when they spring their trap; no Perception + Alertness rolls are made for them.
A character taken by surprise has no Defense in the first turn of combat. His Defense trait is not subtracted from attackers' dice pools. His armor (if any) still is, though.
Targets already involved in combat cannot be ambushed.
