We all like to give referees the benefit of the doubt. They undoubtedly have a very tough job and without the video replays that we all enjoy while watching the game on TV, it's little wonder that they occasionally make mistakes.
Sometimes, though, it's difficult to be so forgiving. Every once in a while, a referee will make a mistake that is so glaring that you wonder if the problem was that they didn't see the incident in the first place, rather than not being able to watch it over again.
Such indiscretions can be forgiven during a park game, but some such moments occur on the biggest stages of all, when league titles, relegation and World Cups are on the line.
Here are soccer's 20 most notoriously bad referee calls.