When visiting or helping in another player's Keep, you can choose to Sabotage a room. This sets the room on fire, forces everyone to exit the room, and makes it harm whatever it was boosting for a period of time.
  • Drag & drop your Noble in a room, to start helping boost it
  • Tap on your Noble that helps boost a room
  • Tap "Sabotage"
If you are caught your rapport with the other family is reduced and your Noble returns home right away.
If you are not caught they are informed someone sabotaged their room, but they are not told who did it.