The rally stops, but the score does not change. In badminton, that can be a let: play since the last service is disregarded and the player who served last serves again.
Law 14 in the BWF Laws of Badminton sets out the situations and the effect of a let. It is different from a fault, which has a scoring consequence under the rally-scoring system.
Look at why play stopped
Examples in the laws include a service delivered before the receiver is ready, specified cases of the shuttle becoming caught in the net after the service has been returned, and the shuttle disintegrating so that its base separates completely. Unforeseen or accidental situations can also require a let.
The details matter. A shuttle merely touching the net and continuing across is not automatically a let. Nor can a receiver normally attempt a return and then rely on having been unready; the service-readiness rule must be read with the relevant circumstances.
In an umpired match, follow the official’s call. Without an umpire, the laws allow a player to call a let, but that is not a general option to replay a disappointing shot. Agree on the rules and communicate clearly before continuing.
Consider an invented club example: another court’s shuttle unexpectedly enters the playing area and interrupts the rally. Stop safely, establish the situation and apply the appropriate rule. Do not continue a hazardous chase merely to avoid losing the point.
Restart without changing the score
Before the next service, confirm the score and server. The let does not create a new point or automatically transfer service to the opponent. Keeping this clear prevents a small interruption from becoming a longer scoring disagreement.
If a disputed incident involves a fault as well as an interruption, consult the current laws or the match official rather than applying a slogan such as “everything is replayed”. Competition procedures may also govern how questions are raised.
For spectators, the useful clue is the restart: same score, same server, another rally. The reason for the call still comes from the specific incident and the rule, not from the fact that the shuttle stopped moving.