An Interrupt is a play performed out-of-turn in response to a particular Trigger. Each Interrupt has its own Trigger text that defines the circumstances that permit the Interrupt to be played; these are usually worded in response to enemy activities. In addition to the requirements in the Trigger text, an entity can only play an Interrupt if it is not their turn and they have not already played an Interrupt this turn. Some Interrupts and effects may explicitly override these rules.
Interrupts may also trigger outside of any entity's turn, such as during the round's Draw Phase or Discard Phase. Only one Interrupt may be played per phase in this manner, including only one during the Turn Phase outside of any entity's turn.
There is no limit to the number of Interrupts played per round. An entity may play an Interrupt during every other entity's turn if it has the ability to do so and the Trigger is met.
Some Interrupt entries may include the Automatic keyword. Such Interrupts always fire when the Trigger condition is met, even if the entity would otherwise be unable to play the Interrupt, and even if the entity would prefer not to play the Interrupt.
Stat Tracks may prevent an entity from playing Interrupts or permit additional plays within a turn or phase.
The DM's Guide has details on resolving the timing of Interrupt plays.
See also: Assist