When playing in a golf tournament, it is a rule that each player must have a marker that keeps track of their score.
According to the rules written by the United States Golf Association (USGA) and The R&A, a marker is “the person responsible for entering a player’s score on the player’s scorecard and for certifying that scorecard.”
A marker can be one of several people and is commonly another player, but cannot be a partner of the player.
The Committee responsible for the tournament may choose who each player’s marker is or they will set out the rules that allow a player to choose their own marker.
It’s very common for competitors to mark down each other’s scores during a tournament. This is a quick and easy way to ensure the scores are marked down correctly as the players keep each other honest.