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The Biggest Sports Upsets of the Past Year, According to Polymarket

By Josh Schonwald

Sports upsets are usually measured through rankings, point spreads or reputation. With billions of dollars in annual trading volume, prediction-market data offers another approach.

On Polymarket, outcome contracts generally trade between $0 and $1 and winning shares settle at $1. That means a team trading at $0.10 carries an implied probability of roughly 10%. When that team wins, its pregame price provides a direct measure of just how surprising the result was to the market.

To identify the biggest sports upsets of the past year, Doc's Sports analyzed hundreds of completed, high-volume game and match markets. Each event was ranked by the eventual winner's normalized probability shortly before the scheduled start, with the least likely winners representing the largest upsets.

Across the full dataset, a team or competitor other than the pregame favorite won 36.9% of qualifying events. Among leagues with at least 20 events, MLB recorded the highest underdog win rate, followed by the NBA and NFL.

No result surprised traders more than Bodø/Glimt's 2-1 victory over Inter Milan on February 24, 2026. The Norwegian club entered the UEFA Champions League match with an implied 8.5% chance of winning. Bodø/Glimt also produced the second-largest upset in the analysis, defeating Atlético Madrid after entering with a 9.5% probability.

The rankings also include long-odds NBA victories by the Washington Wizards, Sacramento Kings and Charlotte Hornets, as well as soccer upsets involving Getafe, Girona, Ajax and Wolverhampton. Together, the results show how prediction-market prices can place surprises across different sports and leagues on the same probability-based scale.

Underdogs Won More Than One-Third of Qualifying Events

Upsets are relatively common in Polymarket moneylines.

Of the 848 qualifying events in our analysis, the pregame favorite won 63.1%. Underdogs won the remaining 36.9%.

Upset rates differ substantially by sport. Among sports with at least 30 qualifying events over the last year, baseball had the highest underdog win rate at 43.6%. Underdogs won 41.2% of American football games and 39.6% of basketball games, compared with 25.0% of soccer matches.

The Biggest Sports Upsets

The largest upset in the analysis was Bodø/Glimt's 2-1 victory over Inter Milan on February 24, 2026. Polymarket traders gave the Norwegian club only an 8.5% chance of winning shortly before the game began.

After a scoreless first half at San Siro, Jens Petter Hauge put Bodø/Glimt ahead in the 57th minute and Håkon Evjen doubled the advantage in the 71st. Alessandro Bastoni pulled one back for Inter four minutes later, but the visitors held on to complete a 5-2 aggregate victory after also winning the first leg 3-1.

It was not Bodø/Glimt's only long-odds victory. Less than a month earlier, the club entered its Champions League match at Atlético Madrid with a 9.5% implied probability and again won 2-1. Bodø/Glimt accounted for the two largest non-draw upsets in the analysis.

The Washington Wizards Clinched the Biggest U.S. Upset

The highest-ranking U.S. result was the Washington Wizards' 126-117 road victory over the Detroit Pistons. The Wizards had only a 10.5% market probability of winning and dressed just 10 players after trade-deadline moves, but reserves Will Riley and Sharife Cooper combined for 38 points. Washington entered the game with a 14-36 record, while the Eastern Conference-leading Pistons were 37-13.

Several other winners carried similarly long odds. The Sacramento Kings and Charlotte Hornets each won with pregame probabilities of 10.5%, while Girona defeated Barcelona with a 10.7% chance and Ajax beat Villarreal after entering at 11.4%.

How Polymarket Probabilities Work

While traditional sportsbooks post odds and accept wagers directly, Polymarket functions as an exchange. Participants buy and sell contracts with one another, and prices are determined by market supply and demand.

Each contract generally trades between $0 and $1. When an event concludes, winning contracts settle at $1 and losing contracts become worthless.

Because of that fixed payout, a contract's price can be interpreted as the market's estimated probability. An outcome trading at $0.10, for example, suggests that traders collectively assign it roughly a 10% chance of occurring.

Prices do not always add to exactly $1 across every possible outcome. Two teams might trade at $0.52 and $0.49, producing a combined price of $1.01.

Doc's Sports therefore normalized the available prices so the probabilities for all possible outcomes totaled 100%. In that example, the two teams' normalized probabilities would be approximately 51.5% and 48.5%.

The analysis used the latest price recorded at least five minutes before each scheduled start. This provided a consistent pregame snapshot while reducing the likelihood that prices recorded after play began would affect the ranking.

Methodology

Doc's Sports analyzed Polymarket sports events scheduled during the 365-day period from July 22, 2025 through July 21, 2026. The universe was limited to completed, full-game moneyline markets in which the listed outcomes represented every possible result of the game.

For each qualifying event, the analysis retrieved historical prices for every available outcome and selected the latest price recorded at least five minutes before the scheduled start. Prices were then normalized so the probabilities for all possible outcomes totaled 100%.

For example, if two teams were trading at $0.52 and $0.49, the raw prices totaled $1.01. After normalization, their implied probabilities would be approximately 51.5% and 48.5%.

The resolved market outcome was used to identify the winner. Games were ranked from the lowest to the highest winning-team pregame probability. Upset scores were calculated as 100 minus the winner's pregame probability. If a team that was ultimately victorious has a pregame win probability of 7%, for example, their upset score would be 93.

Only markets with at least $2.5 million in total reported Polymarket trading volume in reported trading volume were included. The analysis excludes spreads, totals, player props, partial-game markets, futures, and games for which a valid pregame price or confirmed market resolution was unavailable.

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