Many times, being labeled the underdog tells us what is expected before an NBA game, but it doesn’t necessarily tell us how difficult that team will be to beat.
A decade of betting data analyzed by Sports Illustrated provides an interesting example. Looking at the study, we can see teams across the NFL, MLB, NBA, college football and college basketball, followed by analysis of how often each won outright when entering a game as the underdog.
The NFL dominated the overall rankings, with Kansas City, Baltimore and Pittsburgh occupying the first three positions, while the NBA produced considerably lower percentages, but two familiar franchises stood out. Therefore, Boston led all NBA teams with 92 victories from 214 games as an underdog, a 43% win rate. Miami recorded 156 victories from 402 such games, winning 38.8%.
Those numbers become more interesting when viewed through a basketball lens. Neither franchise spent the decade as a traditional outsider. Both enjoyed deep playoff runs, reached NBA Finals and developed reputations for being extremely difficult postseason opponents.
So why were they also so effective on the occasions when the market expected them to lose?
There probably isn’t one answer to the question, but Boston and Miami share several characteristics that help explain why some NBA underdogs are considerably more dangerous than others.
Not every underdog is created equal
There is a common missconfusion, that an “underdog” is really a “bad team”., which is not true, and Boston demonstrates why that doesn’t work like that – the Celtics reached the playoffs every season covered by the Sports Illustrated study. They made six Eastern Conference Finals between 2017 and 2024, reached the NBA Finals in 2022 and won the championship in 2024.
Yet there were still 214 games during the decade in which Boston entered as the underdog.
There are plenty of reasons why this might happen. An otherwise strong team can be playing an elite opponent on the road, dealing with injuries, completing a difficult stretch of its schedule or simply facing a matchup in which the other side is considered more likely to win.
In another example from the study, Miami presents an even more striking example because the Heat were underdogs far more frequently, in fact, across 402 games, they still won outright 156 times.
So why do we put the lable underdogs here, probably we need more context. There is a considerable difference between an underdog because it lacks talent and an experienced playoff team that happens to be a modest outsider in one particular matchup.
Boston and Miami repeatedly occupied the second category.
Coaching can reduce the gap between two teams
One obvious similarity between the franchises is coaching stability.
Miami’s entire period in the study came under Erik Spoelstra, Rosters changed around him, but the Heat maintained a recognizable ability to adjust to opponents, alter defensive coverages and remain competitive without always possessing the more talented lineup on paper.
That matters particularly when facing superior opposition.
Favorites generally have an advantage for a reason, but basketball isn’t played as a comparison of two depth charts. A coach can influence which matchups appear most frequently, where shots are generated and which opposing players are forced into uncomfortable decisions.
Miami’s postseason history during the period provides plenty of evidence that Spoelstra could maximize imperfect rosters. The Heat reached the NBA Finals in 2020 and 2023 and also made another Eastern Conference Finals appearance in 2022.
Boston had more coaching turnover, moving from Brad Stevens to Ime Udoka and then Joe Mazzulla, but maintained a strong organizational identity throughout much of the decade. The Celtics continued building versatile rosters capable of defending multiple positions while developing Jayson Tatum and Jaylen Brown into elite players.
When the talent difference between two teams is relatively small, tactical flexibility can make the underdog label less meaningful than it initially appears.
Star players change what an underdog can realistically do
There is another obvious characteristic shared by dangerous underdogs: somebody still has to create offense when the game gets difficult.
NBA games often tighten late. Transition opportunities disappear, defenses switch more aggressively and possessions increasingly end with one player being asked to create a shot against a set defense.
That is where having an elite individual scorer matters.
Boston spent much of the period with Tatum and Brown capable of taking over possessions. Miami had Jimmy Butler, whose postseason performances became so closely associated with raising his level in important games that “Playoff Jimmy” became part of the league’s vocabulary.
An underdog with a genuine shot creator has a route to winning even when its normal offense isn’t functioning perfectly.
The favorite might generate better opportunities over the first 40 minutes and still find itself in a two-possession game. At that point, one elite scorer hitting three difficult shots can overturn much of what happened before.
That doesn’t make stars immune to bad nights, but it helps explain why experienced teams with high-level creators can remain dangerous even against stronger opposition.
Defensive versatility travels well
Offense can fluctuate dramatically from one night to another. Defense tends to offer a more stable route to remaining competitive.
Both Boston and Miami built successful teams around players capable of handling multiple defensive responsibilities.
That matters against favorites because an underdog’s first task is often preventing the opponent from playing its preferred game.
Switching can take away an action that normally creates open shots. Strong perimeter defenders can make an opposing star work harder for every possession. Help defense can force the ball toward weaker shooters. Physicality can slow down a game that would otherwise become a scoring contest.
A strong defensive team also doesn’t need everything to go right offensively.
If the favorite is held below its usual efficiency, the number of points required to produce an upset falls with it. A poor shooting quarter becomes easier to survive and a close game becomes increasingly susceptible to a handful of possessions deciding the result.
For an underdog, keeping the game close is often the first step toward making the pregame expectations irrelevant.
Three-point shooting can compress the talent gap
Modern basketball introduces another variable that can quickly disrupt expectations: the three-point line.
Over an 82-game season, the stronger team usually has enough time for its quality to show. Over one night, shooting variance can overwhelm the underlying difference between two opponents.
Suppose the favorite creates slightly better shots throughout the game but shoots poorly from three. The underdog makes several contested attempts and gets an unexpected contribution from a role player. A theoretical advantage can disappear remarkably quickly.
Miami demonstrated the importance of three-point variance even in a 2026 game against Boston, making 24 threes despite ultimately losing 147-129.
The result itself went Boston’s way, but the underlying point remains. A high-volume three-point offense gives teams a mechanism for producing outcomes that would be difficult to generate purely through two-point efficiency.
The greater the number of points available from a relatively small number of possessions, the easier it becomes for one exceptional shooting night to change a matchup.
That’s one reason an NBA favorite can be correctly identified as the better team and still lose the game.
Experience matters when the game stays close
There is also a psychological and situational element that statistics don’t capture perfectly.
Experienced teams have played important possessions before.
They have defended after timeouts, managed final-minute situations, handled hostile road crowds and played through stretches when an opponent suddenly builds momentum.
Boston and Miami accumulated enormous amounts of playoff experience during the decade covered by the Sports Illustrated research. That doesn’t guarantee execution, but it reduces the likelihood that the situation itself becomes unfamiliar.
This is particularly important for an underdog because its opportunity often arrives late.
If a favorite fails to establish the expected advantage and the game reaches the final few minutes separated by one or two possessions, the original pregame assessment matters considerably less. What matters now is execution.
Which team gets the right matchup? Who avoids the turnover? Who creates the best shot? Who handles the defensive switch correctly?
A team with players and coaches accustomed to those situations can be far more dangerous than its underdog status suggests.
Price still matters
None of this means Boston or Miami should automatically have been backed whenever they were listed as outsiders.
Sports Illustrated’s study measures outright underdog wins, not whether blindly betting every one of those games would necessarily have produced the best possible return. A 43% win rate also means Boston lost 57% of the games in which it was the underdog.
The important question is whether the probability represented by the available odds accurately reflects the matchup.
That can vary between operators as well as between games. Sports Illustrated covers this wider betting landscape alongside its sports analysis, comparing established sportsbooks with new betting sites and looking at differences in their markets, features and offers. For bettors, however, comparing the number attached to an outcome remains separate from deciding which team is actually more likely to win.
The distinction is important because identifying a dangerous underdog is only the first part of the analysis. There still needs to be enough difference between the market’s expectation and the team’s realistic chances to make that observation meaningful.
Scheduling can create temporary underdogs
The NBA’s schedule also creates circumstances in which the normal hierarchy between teams becomes less reliable.
Back-to-backs, extended road trips and compressed stretches of games can change what should otherwise be a straightforward matchup. A contender playing its fourth game in six nights may present a very different challenge from the same team after two days of rest.
Player availability adds another layer.
A star returning from injury may technically be available but still face a minutes restriction. Another player might be questionable until shortly before tip-off. A team could also choose to rest a veteran during a difficult scheduling stretch.
These situations help explain why evaluating an NBA underdog requires more than comparing season records.
The 50-win team is still the 50-win team, but the specific version taking the floor tonight may not deserve exactly the same expectations.
Matchups matter more than reputation
Perhaps the clearest lesson from Boston and Miami is that reputation alone isn’t enough to understand an underdog.
Some teams have characteristics that make them unusually uncomfortable opponents.
They can defend in several ways. They have players capable of creating difficult shots. Their coaches can change tactics during the game. Their rotations contain enough experience to survive difficult stretches, and they don’t need perfect conditions to remain competitive.
That combination doesn’t guarantee an upset.
It does create more paths toward one.
Sports Illustrated’s decade-long numbers illustrate the result. Boston won 43% of the games in which it was expected to lose, while Miami overcame underdog status 156 times.
The interesting question isn’t simply why bookmakers made them underdogs on those nights. In many cases, the favorite may have fully deserved that status.
The better question is what allowed Boston and Miami to win so many games anyway.
Their histories suggest that the NBA’s most dangerous underdogs aren’t necessarily unpredictable teams hoping for something unusual to happen. They can be experienced, versatile and well-coached teams capable of keeping a game close until the favorite’s supposed advantage becomes much smaller than it looked before tip-off.
Sometimes the most dangerous underdog is simply a very good basketball team facing an opponent expected to be slightly better.
