Reactive Maneuvers can only be done in response to some event that Triggers them. Every Reactive Maneuver will specify what its Triggering conditions are. These could be taking damage, hearing another creature speak, another creature moving away from you, or anything else. Each creature has only one reaction per Turn. However, some reactive abilities are free reactions. These have no limit on the number of times they can be used, so long as their Triggering condition is met every time.