Do Head-to-Head Regular Season Records Matter in the Playoffs?

© Jayne Kamin-Oncea-USA TODAY Sports

Since I’m an obnoxiously determined Devil’s advocate, one of my favorite uses of data is tackling conventional wisdom. For example, one such bit of wisdom that always bugs me is when pundits insist that the best teams are the ones that win close games. In fact, the opposite is true. The most predictive run differential comes in blowouts — the good teams are the ones that are more likely to humiliate their opponents, not squeeze out a close one. This time of year, you start to see a lot of analysis asserting that X team is definitely blessed or doomed come playoff time because of some randomly chosen factor Y. We could do a column a day on these and still have dozens of unwritten pieces by the time the actual playoffs roll around, but let’s focus on a few specific ones, concentrating on who good teams beat rather than how many games they win.

First off, do regular season head-to-head records matter in the playoffs? Since the start of divisional play in 1969, teams that face each other in the playoffs have frequently met in the regular season. Interleague play added eventual World Series matchups to the regular season, and starting in 2023, every playoff matchup will have already occurred during the regular season. Given the sample size of playoff series, if we construct a simple model of series winning percentage that only consists of a team’s regular season winning percentage and its winning percentage in head-to-head matchups, the model horribly inaccurate, with an r-squared of 0.0886 and a mean absolute error of 275 points of winning percentage.

But including head-to-head winning percentage doesn’t really even have a marginal influence on the coin flip; without the head-to-head matchups, the model’s MAE increases to 276 points of winning percentage. Now, a head-to-head record may imply something about a team’s overall strength that isn’t captured in its overall record, but rather than pick up a small sample implication, we can use strength of schedule directly, which does help the model a tiny bit (playoff series are always going to be very uncertain unless we move to best-of-75 series or something wacky).

Just to illustrate this with actual teams rather than a bunch of swanky numbers, let’s look at the 25 most-lopsided regular season matchups of teams that went on to face each other in the playoffs. A team’s expected W-L is derived here solely from the regular season records of the team and its opponents. I ranked the teams by wins-under-even so that the biggest mismatches weren’t littered with a bunch of teams that went 3-0 in their one regular season series:

Biggest Regular Season Mismatches in the Playoffs
Team Opponent Season W Season L Expected W Expected L Actual W Actual L
1983 Phillies 1983 Dodgers 1 11 1.97 2.03 3 1
1988 Dodgers 1988 Mets 1 10 3.20 3.80 4 3
1996 Orioles 1996 Yankees 3 10 2.38 2.62 1 4
2008 Red Sox 2008 Angels 1 8 1.87 2.13 3 1
2003 Twins 2003 Yankees 0 7 1.72 2.28 1 3
2009 Twins 2009 Yankees 0 7 1.19 1.81 0 3
2015 Mets 2015 Cubs 0 7 1.82 2.18 4 0
2005 Astros 2005 Cardinals 5 11 2.58 3.42 4 2
1988 Red Sox 1988 Athletics 3 9 1.62 2.38 0 4
1979 Angels 1979 Orioles 3 9 1.60 2.40 1 3
1980 Astros 1980 Phillies 3 9 2.54 2.46 2 3
1999 Mets 1999 Braves 3 9 2.74 3.26 2 4
1971 Pirates 1971 Giants 3 9 2.18 1.82 3 1
1991 Pirates 1991 Braves 3 9 3.68 3.32 3 4
2020 Yankees 2020 Rays 2 8 1.90 3.10 2 3
2007 Indians 2007 Yankees 0 6 2.05 1.95 3 1
2013 Rays 2013 Red Sox 7 12 1.86 2.14 1 3
1995 Rockies 1995 Braves 4 9 1.63 2.37 1 3
1995 Yankees 1995 Mariners 4 9 2.52 2.48 2 3
1996 Cardinals 1996 Braves 4 9 3.15 3.85 3 4
1998 Indians 1998 Red Sox 3 8 1.92 2.08 3 1
1998 Rangers 1998 Yankees 3 8 1.00 2.00 0 3
1999 Mets 1999 Diamondbacks 2 7 1.91 2.09 3 1
1999 Astros 1999 Braves 1 6 1.84 2.16 1 3
1969 Braves 1969 Mets 4 8 1.37 1.63 0 3
Total Total 63 215 52.2 61.8 50 64

Three of the four teams that were dominated the most by their opponents in the regular season emerged victorious. The 1983 Phillies, 1988 Dodgers, and 2008 Red Sox combined to go 3-29 against the Dodgers, Mets, and Angels, respectively, yet won their playoff series. All told, these 25 teams were expected to go 52-62 based on regular season records and went 50-64. Once you make the model a little more complex and take into account that the 25 most-dominated teams had a few more road games in the playoffs than they did at home and a slightly worse strength-of-schedule, the records are within a win over their 114 games. I can’t conclusively say that there won’t ever be individual cases where head-to-head record matters, but on the macro level, there are probably a lot of things that are more important in the vast majority of cases.

Another question that comes up this time of year — and what it even means never seems to actually be agreed upon past the moment someone makes the statement — is whether it matters which kind of team playoff teams beat up on in the regular season. Is beating up the best teams or the worst teams predictive?

I started off by constructing a simple model of playoff winning percentage based on regular season records and records against the top quintile of teams (.572 winning percentage or better). I got a mean absolute error of 188 points of winning percentage with this model; it gets slightly worse when you only use the regular season record, with an MAE of 212 points. But there’s a big ‘but’ there. Again, teams that beat the best opponents more often, as a group, had a slightly stronger strength of schedule, causing their seasonal records to underrate their overall strength. As mentioned above, it was capturing strength of schedule indirectly rather than directly. Just cutting it out and using regular season record with an adjustment for strength of schedule improves the model and more than eliminates the value of knowing how teams fared against the best quintile of teams.

As before, here are the top 25 playoff teams by how well they fared against the best teams in their league:

Playoff Teams That Dominated the Best
Team Wins vs. Top Quintile Losses vs. Top Quintile Expected W Expected L W L
1999 Braves 34 12 7.55 6.45 7 7
1906 Cubs 30 12 3.99 2.01 2 4
1932 Yankees 40 26 2.48 1.52 4 0
1913 Giants 28 15 2.70 2.30 1 4
1950 Yankees 38 28 2.19 1.81 4 0
2002 Yankees 33 23 2.12 1.88 1 3
1912 Red Sox 27 17 3.57 3.43 4 3
1921 Giants 16 6 3.78 4.22 5 3
1928 Yankees 16 6 2.17 1.83 4 0
1962 Giants 33 24 3.73 3.27 3 4
2002 Braves 18 9 2.72 2.28 2 3
1988 Mets 10 1 3.80 3.20 3 4
1915 Red Sox 26 18 2.91 2.09 4 1
1919 White Sox 24 16 3.49 4.51 3 5
2008 Rays 19 11 8.46 7.54 8 8
1946 Cardinals 16 8 3.14 3.86 4 3
1946 Red Sox 15 7 3.86 3.14 3 4
1959 White Sox 15 7 3.29 2.71 2 4
1951 Yankees 15 7 3.08 2.92 4 2
1918 Cubs 14 6 3.36 2.64 2 4
1997 Marlins 13 5 7.93 8.07 11 5
1917 White Sox 25 18 3.07 2.93 4 2
2011 Yankees 13 6 2.56 2.44 2 3
1997 Orioles 11 4 5.63 4.37 5 5
1954 Giants 25 19 1.59 2.41 4 0
Total 554 311 93.2 83.8 96 81

Before we go, let’s look at the flip side, the playoff teams that dominated the weaker teams in the regular season, those historically in the bottom quintile of teams. The cutoff point here is a .429 winning percentage:

Playoff Teams That Dominated the Worst
Team Wins vs. Worst Quintile Losses vs. Worst Quintile Expected W Expected L W L
1909 Pirates 56 8 4.15 2.85 4 3
1931 Athletics 67 19 3.89 3.11 3 4
1954 Indians 55 11 2.41 1.59 0 4
1908 Cubs 53 13 2.79 2.21 4 1
1939 Yankees 52 14 2.32 1.68 4 0
1915 Red Sox 50 14 2.91 2.09 4 1
1905 Giants 51 15 2.88 2.12 4 1
1931 Cardinals 51 15 3.11 3.89 4 3
1906 Cubs 50 15 3.99 2.01 2 4
1932 Yankees 50 16 2.48 1.52 4 0
1927 Yankees 39 5 2.46 1.54 4 0
1953 Yankees 50 16 2.82 3.18 4 2
1930 Athletics 50 16 3.42 2.58 4 2
1955 Yankees 50 16 3.37 3.63 3 4
1912 Giants 49 16 3.43 3.57 3 4
1944 Cardinals 49 17 3.66 2.34 4 2
1903 Pirates 46 14 3.92 4.08 3 5
1928 Cardinals 38 6 1.83 2.17 0 4
1945 Cubs 38 6 3.95 3.05 3 4
1952 Dodgers 37 6 3.58 3.42 3 4
1910 Cubs 48 18 2.47 2.53 1 4
1919 Reds 45 15 4.51 3.49 5 3
1969 Orioles 42 12 4.54 3.46 4 4
1912 Red Sox 36 7 3.57 3.43 4 3
2019 Astros 38 9 10.16 7.84 10 8
Total 1190 319 88.6 73.4 88 74

In the end, knowing which teams dominated the weak teams did nothing to improve the simple model, adding nothing to our understanding of why some teams win in the playoffs and others don’t (there was no change in r-squared, RMSE, MAE, or, well, anything).

So, we have two bits of information commonly used when talking about playoff matchups: head-to-head record and whether teams are beating up on the best or the worst teams. If you know a team’s overall record — and you absolutely are going to — and a team’s overall strength of schedule in achieving that record, it doesn’t make you better able to predict the coin flip. Even if these data have some hidden meaning on a league-wide level, there are far more important things to care about this time of year, such as whether a team has an ace with a sore elbow or an exploitable platoon split.





Dan Szymborski is a senior writer for FanGraphs and the developer of the ZiPS projection system. He was a writer for ESPN.com from 2010-2018, a regular guest on a number of radio shows and podcasts, and a voting BBWAA member. He also maintains a terrible Twitter account at @DSzymborski.

14 Comments
Oldest
Newest Most Voted
Inline Feedbacks
View all comments
EonADS
26 days ago

I’ve always wondered if the teams who have the most close, difficult games would struggle more in the playoffs. Logic says yes; any team that has to struggle for wins is likely to do worse, and the fatigue factor is likely higher. On the other hand, a (kinda sideways) argument could be made that teams who have experience in pressure cooker games will do better in the pressure cooker that is the postseason.

HappyFunBallmember
26 days ago
Reply to  EonADS

A couple of big assumptions there are (1) that close regular season games have a similar pressure level as close postseason games, and (2) that there is a meaningful difference among pro ball players in their ability to handle pressure.

(2) has been failed to be proven (I won’t say DISproven, just never proven) over and over again in the realm of clutch performance.

If teams who have lots of close games struggle in the postseason, the most likely explanation is that the existence of all those close games means they weren’t really all that much better, but more likely simply fortunate to win more often than not. Come postseason matchups against stronger opposition, and absent continued good fortune, bad things happen.

Last edited 26 days ago by HappyFunBall
Doug Lampertmember
26 days ago
Reply to  HappyFunBall

If there is a “win close games” skill, it is almost certainly in the top 3-4 arms in the bullpen.

It’s quite possible that you win lots of close games in the regular season by having a good top end of your bullpen in the regular season.

It’s quite possible that you win lots of close games in the postseason by having a good top end of your bullpen in the post season.

But these are likely to be mostly different players. The closer is probably on both lists. But the number 4 and 5 starters are in the bullpen most post-seasons, and it isn’t unusual to see the ace starter playing out of the bullpen on short rest in an elimination game.

Thus, I wouldn’t expect much correlation between winning close games in the regular season vs. the postseason (quite aside from the fact that the sample sizes for the postseason half tend to be very small).