Sports have a funny way of making predictions look foolish, because a favorite can dominate for weeks and suddenly fall apart against a team nobody gave much of a chance. Many things can stand behind this, for example, one injury changes the entire complexion of a game, or an opposite player catches fire at exactly the right moment and seems unstopable. Sometimes there isn't even an obvious explanation to what happens, it just happens - the supposed underdog simply turns up and wins against the odds, leaving everyone with jaws dropped down.
Over a single game, that's just sport, you just had a bad day, and you move on, but when the same teams keep doing it for years, it becomes much more interesting. That’s what we are going to cover today.
Research published by Sports Illustrated examined ten seasons of betting data across the NFL, NBA, MLB, NCAA basketball and NCAA football to identify the teams that performed best when bookmakers had them as underdogs. This expert study covered results from 2016 through 2026, and some familiar names repeatedly appear among the teams that were hardest to write off, one of the clearest examples is the Kansas City Chiefs, who lead the entire ranking, but they are far from alone.
Kansas City has turned being an underdog into an advantage
It's difficult to associate the word "underdog" with the modern Kansas City Chiefs, as they are three times Super Bowl winner during the period covered by the research.
Yet on the relatively rare occasions when bookmakers expected Kansas City to come up short, the Chiefs had an extraordinary habit of proving them wrong, and Sports Illustrated’s data showed, that Kansas City entered 30 games as an underdog and won 20 of them, meaning a win rate of 66.67%, the highest of any team included in the study.
There is an obvious caveat. Thirty games isn't a particularly large sample compared with teams from sports such as baseball and basketball, but that's partly the point, as Kansas City became increasingly dominant, there simply weren't many occasions when the Chiefs were considered outsiders. But when those occasions did arrive, they still won two-thirds of the time.
Baltimore and Pittsburgh weren't far behind
The next two teams make the NFL's presence at the top even more striking – we will take a look Baltimore recorded a 61.9% win rate when entering games as the underdog, winning 26 times, making them stand at exactly 60%.
The Steelers' record is particularly interesting because of the volume involved, as they weren't outsiders on just a handful of occasions. Pittsburgh won 45 games from the underdog position during the decade analyzed, which paints a slightly different picture from Kansas City's record, as the Chiefs were rarely expected to lose and frequently responded by winning anyway. Pittsburgh found itself on the wrong side of expectations considerably more often, yet still managed to turn 45 of those games into victories.
It is the sort of statistic that fits neatly with the reputation Mike Tomlin's Steelers have developed, even when Pittsburgh hasn't looked like a genuine championship contender, writing the team off has often been uncomfortable.
An underdog isn't necessarily a bad team
There is something else the rankings make clear: "underdog" can be a misleading word, as we tend to associate it with Cinderella stories, enormous upsets and teams somehow overcoming overwhelming odds, but betting markets aren't quite that simple.
We must say, that a strong team can be an underdog because it is playing another elite opponent, or the bookmakers has taken into consideration venue, injuries, recent form and player availability, which can all influence the outcome of the game. Expectations can also change significantly between the moment a market opens and the beginning of a game.
That's important context for the Sports Illustrated findings because the research isn't identifying the worst teams that somehow managed to win, it is to extent measuring what happened when the market favored their opponent.
Sports Illustrated regularly covers those markets alongside its wider sports reporting, including comparisons of operators, promotions and offers such as the bet365 sign up bonus available to their broad visitor base. But the decade-long underdog data demonstrates something more fundamental about betting probabilities, which is being favored is never the same thing as being guaranteed to win.
The Astros did it 178 times
Move from football to baseball and the numbers suddenly become much larger, which is probably inevitable when an MLB team plays 162 regular-season games rather than 17, but Houston's record is impressive nonetheless that fact.
The Astros ranked first among MLB teams in Sports Illustrated's research, winning 178 games when listed as underdogs, and their 51.3% win rate made Houston the only MLB team in the study to win more than half of its games from that position.
That achievement becomes even more interesting when placed alongside Houston's wider success. The Astros team managed to reached four World Series between 2017 and 2022 and won championships in 2017 and 2022, meaning that this was not a franchise spending the decade waiting for occasional miracle victories.
Instead, Houston provides another example of a highly successful team remaining dangerous on the occasions when the market moved against it. The Milwaukee Brewers deserve a mention for a different reason with their 49.5% success rate was slightly lower, but they recorded an enormous 352 victories as underdogs.
Boston leads the NBA
The same pattern appears in basketball, which was probably already expected by the readers. Boston finished first among NBA teams with a 43% win rate as an underdog, winning 92 of the 214 games in which bookmakers favored its opponent, but we must say again, that "underdog" feels strange next to the Celtics.
Boston spent much of the decade competing deep into the postseason, reaching the Eastern Conference Finals repeatedly before winning its 18th NBA championship in 2024, and yet even elite teams aren't favored every night across an 82-game season. Road games, injuries, back-to-backs and meetings with other championship contenders create plenty of opportunities for the market to lean toward the opposition, but Boston simply proved better than any other NBA team in the study at winning when that happened.
Miami provides another interesting comparison. The Heat were underdogs far more frequently, entering 402 games from that position and winning 156 of them. Their 38.8% success rate placed them among the NBA's strongest performers when expectations were against them.
College football produced some familiar names too
If there's a recurring theme here, college football certainly doesn't break it, and we will dive deep into Clemson, a team that recorded the highest underdog win percentage in the NCAA football portion of the research at 57.1%. Alabama came next at 55.6%, and those are two programs that spent much of the decade competing at the very top of the sport.
Clemson won national championships following the 2016 and 2018 seasons, while Alabama collected titles following the 2017 and 2020 campaigns. Yes, the samples are small, Clemson was listed as an underdog only 14 times, while Alabama faced that situation just nine times, but there is clear evidence, that scarcity itself says something about how those programs were viewed during the period.
Sometimes the biggest mistake is writing off a winner
The research ultimately produces an interesting contradiction, because when you look through the leading underdogs and you don't find a collection of hopeless teams enjoying occasional moments of glory, instead you find the Chiefs, Ravens, Steelers, Astros, Celtics, Clemson and Alabama.
Many of them spent the same decade winning divisions, reaching championship games and collecting trophies, and perhaps that is what makes the data more revealing than a straightforward collection of famous sporting upsets. Being an underdog says something about expectations for one particular game. It doesn't erase everything that makes a strong team difficult to beat.
Kansas City proved that better than anyone - thirty times, the Chiefs entered a game with the market favoring the other team. Twenty times, they walked away as winners.
After ten years of data, there are some teams you probably shouldn't write off quite so quickly.
