Dr. Brian Kriegler’s Statistical Take on MLB Playoff Chaos: Five Reasons Why Underdogs Roar in October

Under the current playoff format featuring 6 AL and 6 NL teams, the road to the World Series becomes a war of attrition, and chaos is virtually guaranteed.

A High-Level Look at Wild Card Teams’ Postseason Results

The track record of wild card teams has long fascinated me. Over the past 30 years, they have consistently thrived despite not winning their division:

• Across 66 LDS that have featured one wild card, the wild card advanced to the LCS 34 times, i.e., 51.5%.
• Across 60 LCS, 30 included one wild card, while two (the 2022 and 2023 NLCS) featured two wild cards. Altogether, wild cards have advanced to the World Series 16 times, i.e., 26.7% of all LCS and 46.7% of those that included one wild card.
• In the World Series itself, wild cards have won 8 championships in the past 30 years, i.e., 26.7%.

These numbers show that wild cards are not just spoilers; they are legitimate contenders once October begins. What follows is a deeper analytical dive. By blending probability theory with baseball context, we can see more clearly why October outcomes can defy popular expectations.

1. The Differences Between Playoff Teams Generally Are Thin

Regular season win-loss records capture how well a team performs across a wide range of opponents, ballparks, climates, and circumstances spanning April through September. The margins between division winners and wild cards usually amount to only a few wins over 162 games.

Over the past 30 years, division champions average 95 regular season wins (interquartile range: 92 to 98 wins), and wild cards average 91 wins (interquartile range: 89 to 94 wins).[1]  There are two key takeaways from these summary statistics.

• First, these gaps are narrow. Over a 162-game season, a team with 91 wins likely could have picked up a few additional victories just as easily as a team with 95 wins could have lost a few close games.
• Second, a team’s win-loss record captures how well a team performs across a wide range of opponents, ballparks, climates, and circumstances over 162 games. That’s not necessarily indicative of, or equivalent to, how a team matches up against elite competition.

With respect to the second bullet point above, a division champion might rack up wins against relatively average and weaker clubs but struggle against the teams that qualify for the playoffs. Or, they might be loaded with left-handed hitters but vulnerable when facing left-handed pitching, something they didn’t have to face as often during the regular season. In a seven- and especially three- or five-game series against the best teams in the league, weaknesses will be magnified.

📌 Example: Atlanta Braves from 1991 to 2005
During the 1990s and early 2000s, the Braves averaged 96 wins and captured 13 straight division titles behind three future Hall of Fame pitchers (Glavine, Maddux,[2] and Smoltz)[3] and an offense that was anchored by Chipper Jones, Andruw Jones, and Javy Lopez. Yet their postseason success was intermittent: one World Series title (1995), four World Series losses, four NLCS exits, and five NLDS eliminations. Come October, the gap (if any) between these Braves teams and the other top MLB clubs was far less noticeable.

2. Rosters Evolve Over the Course of the Season

The July 31 trade deadline can reshape rosters.[4] Some teams add difference-makers while others make only minor adjustments. By October, playoff lineups can look quite different from the ones that built the standings. As a result of these player transactions, October often showcases teams that are stronger, deeper, or simply different from the ones fans watched all summer.

📌 Example: 2022 NLDS, San Diego Padres (89-73) vs. Los Angeles Dodgers (111-51)
At the trade deadline, the Padres made a splash by acquiring Juan Soto, Josh Hader, and Josh Bell. The Dodgers’ biggest move, Joey Gallo, had little impact. By October, San Diego looked like a new team. They stunned their heavily favored rivals despite having lost 14 of 19 matchups against them during the regular season.

3. Short Playoff Series Invite Chaos

From a purely statistical standpoint, the shorter the playoff round, the greater the variance. Suppose the “better” team has a 60% chance of winning any given game. Within this framework and using standard probability techniques, this “better” team has a 68% chance of winning the best-of-five LDS (and a 32% chance of losing the best-of-five).[5] That’s the likely outcome but far from a lock. Across the two League Division Series each year, there’s a 54% chance that at least one wild card will advance.[6]  

📌 Example: 2014 San Francisco Giants (88-74) and Kansas City Royals (89-73)
Both wild cards beat top seeds in five-game Division Series. The Royals swept the 98-win Angels in the ALDS, and the Giants ousted the 96-win Nationals in the NLDS. Both the Giants and Royals made it to the World Series, and San Francisco went on to capture the title with a Game 7 victory.

4. Fatigue Entering the Postseason Is Not Captured in Season Records

The 162-game regular season provides a rich dataset on every player and team. But those six months, plus a month of Spring Training, are exhausting for managers, coaches, players, and staff. Which playoff team will be healthy and peak at the right time? It’s not necessarily the one with the most wins. Pitcher workloads, nagging injuries, and bullpen depth are hidden variables that the standings don’t capture. October often rewards teams that managed health and workload as carefully as wins.

📌 Example: 2022 Phillies (87-75, 3^rd place)
Underdogs on paper, the Phillies entered October with their rotation lined up, bullpen roles set, and stars healthy. They stormed past the Cardinals, Braves, and Padres — each of which finished with more wins than the Phillies during the regular season.

5. Momentum is Real and Measurable

Some teams simply get hot leading up to the playoffs.

Consider a club that squeaks into the playoffs but closes the season on an 18-6 run while beating quality opponents. That team is likely executing cleanly, getting contributions across the roster, and playing with confidence. By contrast, a 100-win team that stumbles to a 12-12 September may already be showing cracks. In October, recent form often outweighs six months of averages.

📌 Example: 2019 Nationals (93-69, 2^nd place)
After a dreadful 19-31 start to their season, the Nationals surged to a 74-38 record the rest of the way. They carried that momentum into October and captured their first World Series title.

Concluding Thoughts: Why Chaos Is the Norm in October

In the postseason, every team starts fresh at 0-0. Regular season win totals, hot streaks, and historical pedigree set the stage. At the same time, probability theory reminds us that anything can happen in a short series. A handful of games against the league’s best can erase a summer’s worth of separation. Matchups, health, and form in the moment often matter more than 162 games of evidence. It’s what makes October baseball both unpredictable and fun to watch from start to finish.