What is the greatest upset in sports history?
The greatest upset in sports history is a matter of opinion, but some of the most commonly cited contenders include:

* **U.S. Olympic hockey team over Soviet Union in the Winter Olympics, 1980**. The United States was a group of college kids, while the Soviet Union was a team of professional players who had won the gold medal in the previous four Olympics. The Americans pulled off a stunning 4-3 victory, which is known as the Miracle on Ice.
* **New York Jets defeat Baltimore Colts, Super Bowl III, 1969**. The Jets were a 17-point underdog against the Colts, who were considered one of the greatest teams in NFL history. The Jets won 16-7, giving the AFL its first Super Bowl victory.
* **Villanova tops Georgetown to win 1985 NCAA championship**. Villanova was a 16-seed, the lowest seed ever to reach the NCAA championship game. They upset top-seeded Georgetown 66-64, becoming the first team from outside the power conferences to win the title.
* **Buster Douglas KOs Mike Tyson for heavyweight championship, 1990**. Tyson was the undefeated heavyweight champion, and Douglas was a 42-1 underdog. Douglas knocked Tyson out in the 11th round, one of the biggest upsets in boxing history.
* **Appalachian State football over Michigan, 2007**. Appalachian State was a 31-point underdog against Michigan, who was ranked #5 in the country. Appalachian State won 34-32, one of the biggest upsets in college football history.

Ultimately, the greatest upset in sports history is the one that most surprised and captivated the public. These are just a few of the many upsets that have had a lasting impact on sports fans.
Interesting.
Can you tell me something similar for the first half of the XX centory?
Sure, here are some of the greatest sports upsets of the first half of the 20th century:

- **Chicago White Sox over Chicago Cubs, 1906 World Series**. Strictly by the difference between the teams’ winning percentages, this marks the biggest upset in World Series history. The Cubs had won 116 games, a record that still stands today (although it was tied by Seattle in 2001) and their .763 winning percentage remains the best in Major League history, yet the White Sox prevailed four games to two in the Series.
- **Francis Ouimet defeats the British pros, 1913 U.S. Open**. Ouimet was a 20-year-old amateur who had a 10-year-old boy as a caddy. He was never expected to even compete with the top professionals in the event, but managed to tie the great Harry Vardon and Ted Ray over four rounds, then defeated them in an 18-hole playoff.
- **Upset defeats Man O' War, 1919 Sanford Memorial Stakes**. This is the only race the legendary Man O' War ever lost in the 21 times he went to the post in his career. The appropriately-named Upset was an 8-1 underdog but held off Man O' War to win by a half-length.
- **Centre College defeats Harvard in college football, 1921**. This game is widely considered one of the greatest upsets ever in college football and was named the top upset in American sports in the first half of the century by the Associated Press. The small Kentucky-based college pulled off a 6-0 triumph on Harvard's home field, ending a 26-game unbeaten streak for the Crimson. 
- **James Braddock beats Max Baer, 1935 world heavyweight championship fight**. Braddock, a journeyman fighter who had been forced to quit boxing to support his family during the Depression, earned the title shot after two previous upsets in his return to the ring. He was a big underdog against Baer, but wore down the champion to win by unanimous decision.
- **United States defeats England, 1950 World Cup**. England is considered the birthplace of soccer and fielded a team of full-time professionals that was one of the tournament favorites. The hastily-assembled U.S. team was made up of part-time players, yet the Americans pulled off a stunning 1-0 win in Belo Horizonte, Brazil.
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