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The Los Angeles Dodgers and the Atlanta Braves were both eliminated from Major League Baseball's postseason over the weekend, setting up a most surprising National League Championship Series between the Philadelphia Phillies and San Diego Padres. To label the Phillies-Padres NLCS an unexpected matchup would be within reason. The Phillies (87 wins) and Padres (89) had the fewest wins among NL playoff teams. Only the Tampa Bay Rays, with 86 wins, had a worse record overall and made it to October. 

The additional round of the postseason meant that the path to the NLCS was more cluttered than usual, too. That didn't stop the Phillies from downing the St. Louis Cardinals and Braves, two division winners, nor did it prevent the Padres from slaying the New York Mets and Dodgers, clubs who combined to win 212 regular season contests.

Meanwhile, in the American League, the Cleveland Guardians are trying to pull off a similar feat against the New York Yankees, with their ALDS matchup heading to a winner-take-all Game 5 on Monday night. MLB's final four could include three of the four playoff teams who posted the worst regular season run differentials. (Plus the Houston Astros, who may wind up being the last elite team standing.)

What's behind this October's upset fever? Let's examine three contributing factors.

1. The format

Here's a basic tenant of probability: the smaller the sample, the wider the range of potential outcomes. Want to know who the better team is between the Dodgers and the Braves? Let them play over and over and over again; the larger the sample, the more confidence you can have in the outcome being a reflection of talent, not chance. Conversely, if you were motivated to design the ideal postseason format for the purpose of wreaking havoc, then you could do worse than MLB's new setup. 

Remember, the latest Collective Bargaining Agreement between the league and the players did away with two one-and-done Wild Card Games in lieu of four best-of-three Wild Card Series. A three-game set is less chaotic than one game based on our aforementioned tenet of probability, true, but increasing the sheer amount of these short series also improved the chances of an opening-round upset or two.

Sure enough, three of the four Wild Card Series were won by road teams, or the teams with the inferior regular-season record. That includes the Phillies and the Padres, as well as the since-eliminated Seattle Mariners. The only host to win their Wild Card Series was the Cleveland Guardians, the American League Central champions.

Add in how the best-of-five LDS format is hardly a marathon, and how the two shortest postseason rounds fall back-to-back, and it can feel like the league is being governed by little more than a series of coin flips.

2. The schedule

There's no way of knowing the precise impact the schedule had on the Division Series, but expect to hear more about the quirks as part of the autopsy process. 

For starters, the addition of first-round byes for the top two teams in each league meant they had to endure longer-than-usual layoffs. The Dodgers, for example, finished their regular season on Oct. 5 and did not play again until Oct. 11, or nearly a week later. That time off should be a good thing since it allows injured players to heal and gives those teams a chance to set up their rotations. But it's inevitable that a layoff followed by an inept offensive showing will raise questions about whether or not the time off caused a team's lineup to fall out of their hitting rhythm.

"I think that's something that we could probably debate, but I think leading up to it, even right now, it's not something that we want to look at as an excuse," Dodgers manager Dave Roberts said Saturday night after his 111-win team was sent home. "That's kind of the format the way it is, and you do the best you can in the regular season to put yourself in a position to get home-field advantage, to get the bye in the wild-card round, and it's up to us to kind of prepare ourselves the best way we can to get through a Division Series, and we didn't."

There was also the matter of an AL-specific wrinkle that saw the league deviate from its normal patterns. The ALDS had days off after Games 1 and 2 but not one after Game 4. In the case of the Yankees and Guardians series, a rainout caused them to have consecutive days off ahead of four games in four days. That extra time left the Yankees having played one game in eight days, and negated some of the advantage they gained with the bye, since the Guardians had a chance to set up their pitching staff for Games 2 and 3 in a way they wouldn't have been able to under more ordinary circumstances. 

3. The sport

Let's face it, baseball is a contradiction in a respect. Remember that tenet of probability about sample sizes and range of outcomes? Baseball adheres to it on a macro level better than any other sport by forcing teams to play six months' worth of games; it's hard to fake being either a great or a poor team over that length of time. 

On a micro level? Baseball can be as random as a toddler's walk. Let's put it this way. Other sports have excelled at converting parity into a brand. If the worst NFL or NBA team beats the best three times in a row, that's a headline; in baseball, that's May. 

To wit, the Dodgers -- the team with the fourth-best single-season record since 1900 and the best run differential since the 1939 New  York Yankees -- were swept in a three-game series by the lowly Pittsburgh Pirates over the summer. The Dodgers didn't fire anyone. They didn't hire a crisis management team. They just kept it moving because they know that's how baseball works -- and they certainly, without any doubt or hesitation, know that remains true in the postseason.