What history tells us about predicting the NBA Playoffs’ first round series

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Is winning the regular season series with your playoff opponent really an indicator of postseason success?

Playoff predictions are far more simple than people make them out to be, especially in the first round — at least if recent history is any indication.

Over the last eight years — since the Stephen Curry-led Golden State Warriors started a 3-point shooting explosion that has changed pace of play in the league — top-three seeds advance out of the first round at a really reliable rate. Yet we spend so much time and energy in the days leading up to the playoffs diving back in and seeing how the regular season games and matchups went down.

Those matchups often lead to braze predictions of upsets and believing that the lower seed has a good chance simply because they fared well in the regular season or had one tactical advantage that could make a series close.

I wanted to test the hypothesis that the regular season matchups were actually fairly irrelevant in predicting series winners. Those games might tell us, I believed, that there are key matchups or stylistic challenges for how the series could be played. But the real question is whether underdog teams who fare well in the regular season have any sort of advantage coming into the playoffs.

Instead of breaking it down across the board, it is prudent to go by first-round matchup historically. The disparity of talent and success between top seeds and eight-seeds is far different than a No. 4 vs. No. 5 matchup. Perhaps a deep dive into each series in the post-3-point explosion era could reveal something new about how to predict the winners in a tightly-contested 2023 playoff setting.

No. 1 seed vs. No. 8 seed matchups

Top seeds: 16-0 since 2015

It’s been over a decade since a top-seeded team in either conference has failed to make the second round of the NBA Playoffs. The last eight seed to upend their foe was the 2012 Philadelphia 76ers, who capitalized on the torn ACL of Derrick Rose suffered in Game 1 of that series. Plain and simple, these upsets rarely happen — especially over the last decade where the dominance of the Golden State Warriors and LeBron James’ teams in the East was clear.

With as large of a gap in win totals as there tends to be between these first-round adversaries, regular season matchups don’t tend to be an indicator of much. Only one eight-seed (the 2016 Detroit Pistons) actually won their regular season matchup with their opponent (the LeBron Cavaliers). Even in that regular season footnote of history there are asterisks. One of the Pistons victories was the regular season finale, where the Cavaliers sat all their important players. Cleveland went on to unceremoniously sweep Detroit in the playoffs.

Instead of predicting a series victory, perhaps we can use the regular season results to see how long the series will go. That’s also a tough pull, as no eight-seed has even forced a Game 7 in this timeframe. Only a quarter of the series went to a Game 6. Two of them featured an even regular season split of head-to-head contests. Translation: the only way a series typically gets past five games is if the lower seed won two regular season games.

The Milwaukee Bucks split their regular season series with both the Chicago Bulls and Miami Heat. Either way the final play-in game goes, history would suggest that the underdog can steal at least one game. Every recent team to win two regular season games against their top-seeded foe has pushed the series to six. Out West, the Denver Nuggets split 2-2 with the Minnesota Timberwolves but took down Oklahoma City three times out of four. Similarly, history would indicate that we’re unlikely to see a sweep.

No. 2 vs. No. 7 matchups

Top seeds: 16-0 since 2015

Similar to those 1 vs. 8 matchups in the first round, the 2 vs. 7 series have not given a ton of parity. The last time a two-seed was dropped in the opening series was in 2010 when the Dallas Mavericks lost to the San Antonio Spurs.

We’re getting slightly closer to parity, though. Six of the last sixteen matchups between the 2 and 7 have seen even 2-2 splits in the regular season series. While that’s a high mark, it did not translate to playoff success. This is where bettors and fans need to take the regular season series with a grain of salt. Only three 2 vs. 7 series have even gone to a seventh game, and no team was able to win that seventh game on the road over. In fact, no seven or eight seed has won a first-round do-or-die game on the road since the NBA expanded to a best-of-seven series back in 2003.

With the Boston Celtics sweeping Atlanta 3-0 in the regular season, a Hawks upset would literally buck every historical trend. Where things get interesting is with the Memphis Grizzlies and Los Angeles Lakers series. The Lakers won the regular season 2-1, making them the first seven-seed to earn that distinction in over a decade. The Lakers were one of the best teams after the All-Star Break in the league, and the Grizzlies are very banged up in their frontcourt. If there is one series that could go against the historical dominance of two-seeds in the first round, it’s likely to be this one.

No. 3 seed vs. No. 6 seed matchups

Top seeds: 15-1 since 2015

One of the most surprising findings of doing this research was that only one six-seed has pulled off a first-round upset over the last eight years. That series was in 2018 when the New Orleans Pelicans thrashed the Portland Trail Blazers, sweeping them after splitting the regular season 2-2.

Despite that lack of success in the playoffs, the regular season series’ were much more even between these opponents. Five of the last sixteen 3 vs. 6 series featured teams who each won two matchups against each other before the playoffs. Three lower seeds even won those regular season series, and one of them (the 2019 Oklahoma City Thunder) even swept their season series with Portland.

Strangely, that regular season success has been the opposite of a positive sign for lower seeds. None of those three teams who won head-to-head regular season matchups with a three-seed went on to even force a Game 6! Those 2019 Thunder lost to Portland in five games, and back in 2020, the Philadelphia 76ers got swept by the Boston Celtics after taking three of four in that pandemic-altered season.

This year’s 3 vs. 6 matchup out West features plenty of intrigue. Golden State, the six-seed out West, won the season series with Sacramento 3-1. Their experience could be a major factor in this series, as the defending champions rarely find themselves as the visiting team in the first round.

No. seed 4 vs. No. 5 seed matchups

Top seeds: 8-6 since 2015

When predicting the 4 vs. 5 series, you are probably better off just flipping a coin. Teams have been very evenly split over the last eight years, and the lack of separation between them in the standings is primarily responsible for such parity. This year, only one game separates the Los Angeles Clippers and Phoenix Suns in the 4 vs. 5 matchup our West.

Strangely, only two of the last sixteen showdowns featured teams who split their regular season series. This year’s Clippers and Suns matchup was also even, with both teams winning two, including Los Angeles beating Phoenix in the regular season finale last weekend.

Most of the time, these series feature one team who wins the battle head-to-head over the first 82 games.

Those teams are 5-9 in the first round.

If history is any indication, it’s actually not a smart bet to predict the winner of a 4 vs. 5 series simply because they fared better head-to-head in the regular season. That could be good news this year for the Cleveland Cavaliers, who lost three of four to the New York Knicks this year.

The deeper dives into the data reveal that very few trends from the regular season actually exist. Teams to sweep their regular season series went 2-2 in the first round, with the most recent loss being the Knicks in 2021, who beat the Hawks all three times before getting run out of the Garden by Trae Young in the playoffs. Over the last eight years, four 4 vs. 5 matchups have gone to a seventh game. The team who won the regular season matchup ended up losing all four Game 7 opportunities.

As we get to playoff predictions, so much analysis is centered around dissecting the regular season matchups. In the first round, that often doesn’t provide too much value. If seeding trends are any indication, the first round is pretty much all chalk from the top seeds and a toss-up in the 4 vs. 5 matchup. With the parity in the Western Conference and injuries to players on the Memphis Grizzlies, this year could be the exception to the rule in that regard. However, it’s a pretty safe bet that the top seeds will move on without much hassle — even if they didn’t fare very well in the regular season.