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MLB’s Postseason Is A Tale Of Two Leagues

Remember all those big favorites going into the MLB postseason? The record-tying four 100-plus win teams from the regular season? The 20-win gaps between best and worst seeds in each league? The theoretical advantage of a first-round bye for top teams under MLB’s new playoff system?

Turns out only one league got the memo about the big disparity between baseball’s haves and have-nots this season.

Over in the National League, chaos has reigned supreme. After the lower seeds won both wild card matchups, the San Diego Padres and Philadelphia Phillies kept that energy going in the divisional round as well, knocking off the heavily favored Los Angeles Dodgers and Atlanta Braves, respectively. Whether you look at the magnitude of those upsets through the lens of regular season win-loss records — both series’ losers had outplayed their opponents by more than 85 points of winning percentage — or our pre-series Elo ratings, the Padres and Phillies pulled off two of the biggest division-series shockers since the round began in 1995:

Two ways of measuring the divisional round’s biggest upsets

Largest gaps in regular-season winning percentage and pre-series Elo rating between an underdog and favorite in MLB division series upsets, 1995-2022

Year Winner Loser Gap Year Winner Loser Gap
2022 SDP LAD -.136 2022 SDP LAD -82.1
2020 HOU OAK -.117 2001 NYY OAK -77.6
2022 PHI ATL -.086 2002 MIN OAK -67.8
2008 LAD CHC -.084 2003 CHC ATL -54.3
2003 CHC ATL -.080 1998 SDP HOU -52.6
2019 WSN LAD -.080 2021 BOS TBR -51.8
2011 STL PHI -.074 1996 BAL CLE -48.9
1996 BAL CLE -.072 2022 PHI ATL -48.7
2017 NYY CLE -.068 1997 CLE NYY -43.5
2012 STL WSN -.062 2017 NYY CLE -40.3

Source: Retrosheet

Meanwhile, over in the American League, a measure of sanity was restored with division series victories by the top-seeded Houston Astros and New York Yankees. It wasn’t exactly easy in either case — the Astros required a pair of one-run victories (the latter of which tied a playoff record at 18 innings) to finish off the Seattle Mariners, while the Yankees had to overcome a 2-1 series deficit against the Cleveland Guardians to advance — but the best teams in the league all season will be playing for the AL pennant.

This sets up an odd juxtaposition between the two championship series. Both are very nearly coin flips in our model — the Astros have a slim edge over the Yankees (54 percent to 46) and the Padres are even slimmer 52-48 favorites over the Phillies — but the combined quality of the two teams in each league could scarcely be more different. The gap between the average Elo rating for the championship contenders in the AL (1578.7) and the NL (1539.9) is 38.8 points. Going back to 1995 again, that’s the biggest differential in the combined quality of LCS teams in one league versus the other in any postseason:

The biggest disparities in LCS quality of the wild card era

Biggest gaps in average Elo rating between MLB teams in one league’s championship series and the other’s, 1995-2022

Year Lg Teams Avg. Elo Lg Teams Avg. Elo Gap
2022 AL HOU, NYY 1578.7 NL SDP, PHI 1539.9 +38.8
2021 NL ATL, LAD 1587.1 AL HOU, BOS 1549.5 37.6
2007 AL BOS, CLE 1569.3 NL ARI, COL 1537.3 32.0
2019 AL HOU, NYY 1589.0 NL STL, WSN 1559.5 29.4
2008 AL TBR, BOS 1566.5 NL PHI, LAD 1537.3 29.2
2009 AL NYY, ANA 1575.7 NL LAD, PHI 1547.5 28.2
2018 AL BOS, HOU 1599.3 NL MIL, LAD 1571.6 27.7
2014 AL BAL, KCR 1554.6 NL STL, SFG 1530.0 24.7
2003 AL NYY, BOS 1560.6 NL CHC, FLA 1536.2 24.3
2011 AL TEX, DET 1558.6 NL MIL, STL 1534.5 24.1

Source: Retrosheet

(Interestingly, it just edges out last year, which featured elite Braves and Dodgers teams in the NL but a less-heralded run by the Boston Red Sox to drag down the AL’s average.)

As a consequence, the ALCS winner should be heavily favored in the Fall Classic, as our model says there’s a 65 percent chance the World Series winner will come out of the AL. But that all depends on which league’s postseason narrative — chaos in the NL, or order in the AL — holds the upper hand by postseason’s end.

Check out our latest MLB predictions.

Neil Paine was the acting sports editor at FiveThirtyEight.


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