An upset occurs in a competition, frequently in electoral politics or sports, when the party popularly expected to win (the "favorite") is defeated by (or, in the case of sports, ties with) an underdog whom the majority expects to lose, defying the conventional wisdom.
The meaning of the word "upset" has long included "an overthrowing or overturn of ideas, plans, etc."
"Upset" also once referred to "a curved part of a bridle-bit, fitting over the tongue of the horse", (now the port of a curb bit), but even though the modern sports meaning of "upset" was first used far more for horse races than for any other competition, there is no evidence of a connection.
[2] Thompson's research debunked one popular theory of the term's origin, namely that it was first used after the surprising defeat of the horse Man o' War by the racehorse Upset in 1919 (the loss was the only one in Man o' War's career).
Below is a list of elections which have extensively been described as upsets by a number of major media sources.