Upsets are part of what makes sports exciting. A team nobody expected to win pulls it off, and everyone is shocked. But from a math perspective, upsets are not shocking at all. They happen at roughly the rate the odds suggest. Understanding why helps you think more clearly about every pick.
An upset is just a less likely outcome
If an underdog is priced at +200, its implied chance is 33.3%. That means it should win about one in three times. If it wins, that's not a miracle. It's the one-in-three happening.
Worked example: suppose in one weekend there are 12 games where the underdog is priced at around +200 (about 32% after removing the margin).
- Expected underdog wins: 12 × 0.32 ≈ 3.8
- Chance that no underdog wins: 0.68^12 ≈ 1%
So nearly every weekend, several underdogs will win. That's not a crazy weekend. That's a normal one.
Why some sports have more upsets
Scoring frequency
In sports with lots of scoring, like basketball, the better team's advantage shows up over many possessions. Luck tends to even out within a game. In low-scoring sports like soccer and hockey, a single goal can decide a game, so luck matters more.
Game length and sample size
A baseball game is one sample from a long season. Even great teams lose many games. Over 162 games, the best teams usually win something around 60% and the worst still win a good share. Any single game is close to a coin flip with a lean.
Single-game vs series
A best-of-seven series gives the better team more chances to show its quality. A single game does not. That's why single-elimination tournaments produce more surprises than seven-game series.
Worked example: a team with a 60% chance in each game wins a best-of-seven series about 71% of the time. In a single game, just 60%.
Talent gaps and spreads
In the NFL, parity means many games are close, and underdogs win often. In college football, talent gaps are much wider, so huge underdogs rarely win, though when they do it becomes famous. See college football odds.
Why upsets feel more common or rarer than they are
They feel more common because upsets are memorable. Highlight shows replay them, and they become stories. See the availability heuristic in thinking traps.
They feel rarer when you're picking a favorite, because you think about all the reasons your team should win. Then the upset feels like a shock.
Both feelings mislead. The odds give a better guide.
Underdogs and value
Underdogs aren't automatically good or bad picks. What matters is price versus probability.
Two underdogs:
- A: +300, true chance 22%. Break-even is 25%. Negative value.
- B: +180, true chance 38%. Break-even is 35.7%. Positive value.
Long shots are exciting, but there's evidence in many markets that very long odds are priced less generously than their true chances, sometimes called the favorite-longshot bias. See value betting.
Variance and losing streaks
If you pick underdogs, you'll lose more often, even if your picks have value. Picking +200 underdogs that win 36% of the time is profitable in the long run, but you'll frequently go 0-for-5 or worse.
Chance of five straight losses at 36% win rate: 0.64^5 ≈ 10.7%. That will happen often over a season. Keep stakes small. See bankroll management.
What makes upsets more likely?
- Low scoring: soccer, hockey, low totals in football.
- Injuries to the favorite not fully priced in.
- Weather that reduces the impact of skill, like strong wind.
- Motivation differences: a favorite looking ahead to a bigger game (often discussed, hard to measure).
- Style mismatches that neutralize the favorite's strengths.
A healthy way to think about upsets
Every pick has a range of outcomes. Before a game, ask: "If this were played 100 times, how often would each side win?" When the less likely outcome happens, remind yourself that it was always in the range.
Upsets in a single season
Think about a full NFL regular season with hundreds of games. Even if favorites win around two-thirds of the time, that still leaves a large number of underdog wins, many of them every single week. A season without regular upsets would actually be the strange outcome.
Experience upsets without the sting
On MockSport, you can make free play-money picks on underdogs and favorites and watch how often upsets really happen across a season. With no real money involved, upsets become a lesson rather than a loss. Browse the odds page.
FAQ
How often do underdogs win?
It depends on the price. A +200 underdog should win about one-third of the time. Across many games each week, several underdogs win.
Which sports have the most upsets?
Low-scoring sports like soccer and hockey, and single-game formats, tend to have more upsets than high-scoring sports like basketball.
Are long-shot underdogs good value?
Not usually. In many markets, very long odds are priced shorter than their true chances, a pattern called the favorite-longshot bias.