During their turn, an actor can perform actions by spending potential. Other actors can perform reactions using their potential if they are affected by an action.
Draggomir performs an action during his turn by smashing his hammer against the bandit using the melee combat skill. The bandit can react by making a defence roll to avoid being hit. As it is not the bandit's turn, the bandit cannot perform other actions.
Example Reactions
TODO: Detail attacks of opportunity.