The coach's challenge explained
What the coach's challenge lets a team do, which calls can be reviewed, how a challenge is triggered, and why the number of challenges is limited.
What it is
The coach's challenge gives a team the power to ask officials to take a second look at a call they believe is wrong. Instead of leaving every decision final the moment it is made, the rule lets a coach trigger a video review of a specific play. The officials then watch a replay and either overturn the original call if it was clearly incorrect, or let it stand if the replay does not show a clear mistake.
Which calls can be challenged
A challenge can only be used on certain types of call, not on everything that happens in a game. Typically these include a foul called against the challenging team, a ruling on which team knocked the ball out of bounds, and a goaltending or basket-interference decision. Judgement calls that are not on the reviewable list cannot be challenged, so a coach has to pick the moments where a review is actually allowed.
How it is triggered
To use a challenge, the coach must signal for it promptly, usually by a clear physical signal and by calling a timeout, before play has moved on too far. This immediacy matters, because a review of a play from several possessions earlier would be impractical. Once the challenge is registered, the game pauses while the officials review the footage and announce whether the original call is confirmed or reversed.
Why it is limited
Teams are given only a small number of challenges, often just one, with the possibility of another if the first is successful. The limit exists to protect the flow of the game: if coaches could challenge freely, matches would be constantly interrupted by reviews. By rationing challenges, the rule lets teams correct an important mistake at a key moment without turning every call into a lengthy stoppage.