The Impact of September Performance on October Playoff Outcomes

As the 2026 MLB season hurtles towards its conclusion, a fascinating dynamic emerges among teams vying for postseason contention. Currently, with only two division leaders ahead by less than four games, the competition is intense, especially between the Padres and Diamondbacks, who are locked in a battle for the final National League Wild Card spot. In the American League, a similar race is unfolding among Cleveland, Toronto, and Texas, underscoring a closely contested playoff landscape.

Yet, teams already setting their sights on October face a balancing act. While some squads opt to rest key players and rearrange their pitching rotations for the Wild Card and Division Series, the competitive drive remains strong. The fear of entering the postseason on a losing skid is palpable; last year, the Tigers were the only playoff team with a losing record in September, falling dramatically with a 7-17 record before bowing out to the Mariners in a five-game Division Series.

In contrast, the Yankees showcased a stellar 18-7 record in September 2022, yet fell to the American League champions, the Blue Jays. Their performance that month didn’t translate to playoff success, and that notion hangs in the balance as teams grapple with the importance of late-season momentum.

September Records: A Mixed Indicator of Success

To scrutinize how a team’s September performance translates into playoff outcomes, I examined the records of all 240 teams that reached the Division Series since its inception in 1995, with the exception of the 2020 season. Among these teams, 120 advanced to the Championship Series, and 60 made it to the World Series.

The Indians recorded the best September with a 26-4 mark in 2017, only to be ousted by the Yankees. On the other end, the Tigers and Padres arrived with dismal records (9-15) but still managed to progress in the postseason, with the Padres winning the Division Series and Championship before faltering in the World Series against the Yankees.

Analyzing Correlation: Performance vs. Success

To explore the relationship between September records and postseason outcomes, I assigned a point system to categorize teams based on their success in October: 0 points for losing in the Division Series, 1 for the Championship Series, 2 for losing the World Series, and 3 points for winning it all. The aim was to uncover if strong September performances correlate positively with victories in the postseason.

The data revealed a surprisingly weak correlation:

• Division Series: 0.04
• Championship Series: -0.15
• World Series: 0.06

These numbers indicate there’s hardly any relationship between September performance and playoff success. Historically, teams with the best September records have actually found themselves underwhelming in the World Series, sporting a combined record of 12-16 since 1995.

Examining High and Low Performers

When narrowing the focus to the 60 teams with the most and least successful September records, a trend emerges. Teams with a win percentage of .667 or higher performed reasonably well against those with a record of .538 or lower. Specifically, these stronger teams recorded a 15-9 record in postseason matchups, showing promise with an 11-7 outcome in Division Series and a commendable 2-2 in the Championship Series.

But this leads us into a nuanced territory—often the playoff success can relate more to a team’s overall quality than to how well they performed specifically in September. For example, the Astros’ victory over the Phillies in 2022 showcased a dominant 106-win team overcoming a less impressive 87-win opponent, despite their uneven September ends. Even with the Astros’ solid 22-9 performance in September compared to the Phillies' 14-17, the true strength arguably lay in their regular-season accomplishments prior to the final month.

Conclusions: Perspective on September's Role

Ultimately, it's clear that teams in playoff contention shouldn’t dwell too heavily on their September records. Superior or inferior performance during that month seems not to be a reliable predictor of postseason fate. Instead, the message is clear: maintaining composure and focusing on genuine team capabilities will serve them better in the playoff race.

The postseason imminently approaches, and while September records can offer some insight, they aren’t the definitive roadmaps for success in October's unpredictable landscape.

¿Cerrar sin hacer ruido es tan bueno como hacerlo con estruendo?

Published on Baseball Prospectus.