When a
combat starts, if a character was not aware of his or her enemies and they were aware of the character, that character is surprised. Likewise, a character can surprise his or her enemies if the character knows about them before they're aware of the character.
If some but not all of the combatants are aware of their opponents, a surprise round happens before regular rounds begin. The combatants who are aware of the opponents can act in
the surprise round, so they roll for
initiative. In
initiative order (highest to lowest), combatants who started the battle aware of their opponents each take an
attack action or
move action during
the surprise round (see
Action Types, below). If no one or everyone is surprised, a surprise round does not occur.