Does Head-To-Head Regular Season Record Matter in the Playoffs?
You often hear it cited: a team won the season series and now they’re facing off in the playoffs. How will it impact their chances in the playoffs? Here at Her Hoop Stats, this is exactly the kind of question that gets us excited. We thought we’d dig into the archives to see what history tells us.
In the opening round of the 2019 playoffs, the Chicago Sky will face the Phoenix Mercury and the Minnesota Lynx will face the Seattle Storm tonight. In the regular season, Chicago won their series against the Mercury 3–0. Seattle won theirs against the Lynx 3–1. Does their head-to-head record really matter?
In the single-elimination games, the answer is clearly no. Dating back to the start of the WNBA in 1997, there have been 17 single-elimination games. Of those games, three of the corresponding regular-season series have ended in a 2–2 game tie and are not included in our analysis. That leaves 14 relevant games in WNBA history. It’s a small sample size, but just 43% of the teams that have won the regular-season series have gone on to win the single-elimination game.
Of course, never before has a team been in the situation of the Chicago Sky: playing a single-elimination game against an opponent they swept in the regular season. However, if we instead look at one-game series by the seed of the opponent, the higher seed went 11–6 and won the playoff series 65% of the time. It is not surprising that the seed appears to be a better indicator of playoff success. A team’s seed represents a larger sample size of games, spanning the whole season.
Take, for example, Washington and Connecticut this year. Connecticut won the regular-season series 2–1. However, one of those Sun victories came without Elena Delle Donne on the floor. They also haven’t played each other in two months. Those are just two reasons why a handful of games in the regular season don’t predict playoff performance effectively.
Of course, if Washington and Connecticut do play each other in the playoffs it will be a five-game series. Do regular-season head-to-head results matter more in a longer series?
The answer is not really. Throughout WNBA history, the winner of the regular-season series has won the five-game playoff series 63 percent of the time. While more favorable for the regular series winner than in a shorter series, the regular-season results are not incredibly meaningful given the sample size.
In WNBA history, teams have faced off 16 times in a five-game playoff round after a team won the season series. In four others, the regular-season series was a tie. Here are the detailed results for the 16 examples of a regular-season series winner:
On the other hand, seeding/record is clearly more important in a five-game playoff series. The higher seed/team with the best regular-season record has gone 15–5 when the teams face off in the playoffs. That’s a 75% winning percentage.
Interestingly, sweeping a regular-season series does seem to be a little more predictive of playoff advancement. Overall, there have been 38 playoff series of varying lengths where a team swept the corresponding regular-season series. In those cases, the team who won the regular series advanced in the playoffs 76 percent of the time. Here’s how those results stack up historically by playoff series length:
With the first round set, we can already compare Chicago/Phoenix and Seattle/Minnesota head-to-head results to this data. If you are looking to do so later in the playoffs, here’s the full breakdown of 2019 regular season series results for playoff teams. To read this chart, pick the row for the team you’re interested in and then choose their opponent based on the column. For example, Connecticut fans can see they went 1–2 against the Sparks and 2–1 against the Aces by reading the second row. Our advice for the Sun would be not to worry about those head-to-head records, though, the fact they’ll be the higher seeded team is far more important.