Other forms: refs
A ref is the person who arbitrates conflicts during a sports match or game, and makes sure everyone's playing by the rules. If your team gets a bad call, blame the ref.
Ref is shorthand for referee, which until the mid-1800s meant "a person who examines patent applications." By 1856, a referee was a baseball official, and the nickname ref followed soon after. You can use this word as a noun, for the person wearing a striped shirt and running up and down the edge of the football field — or a verb, to mean "officiate at a sporting event."