What can be checked on video in water polo, and can a coach ask for it?

• Who decides: "The final decision is always made by the referees." Only the referee can ask for a review. The video assistant and the delegate can alert the referee.
• What the referee may review: goal or no goal; a goal scored as the possession clock or the period ends; errors at the table or in the electronic system; a shot at the end of a period while a player is excluded; a violent action; interference with a penalty throw; improper entry or re-entry; corner throw or goal throw.
• When: at a suitable moment, and no later than the first attack after the incident.
• The coach's challenge: each coach may challenge one call a match. The list covers an uncalled violent action, a penalty foul called or not called, and the situations above when they have not been reviewed already.
• Not twice: a coach cannot challenge a decision the referee has already reviewed on video.
• The signal: the coach presses the timeout button or sounds a horn and shows a green flag, or draws a square with the index fingers.
• If it succeeds: the clock goes back to the moment of the incident. Goals, personal fouls and timeouts from the time put back are wiped out. Cards and exclusions for violent action or misconduct stay. The coach may challenge once more.
• If it fails: the match carries on, and the team has no further challenge.
• A challenge that is not allowed: a yellow card for the coach, or a red if they already have a yellow.

The glossary has the video assistant referee and violent action.

Much of the game happens under water or in a crowd in front of goal, where two referees on the side cannot see everything. Video is kept for the decisions that most change a result, and the single challenge stops coaches from using reviews to break up the game.