Home-court advantage matters less than you think

The Portland Trail Blazers will likely face off against the Utah Jazz in the 2019 NBA Playoffs in the 4/5-seed matchup. Other outcomes are possible, but this series is the most likely.

If that happens, the Blazers should have an advantage since they’ll get an extra game at the Rose Garden, right? Let’s take a look at the data to see if that’s true.

4/5 Playoff Matchups and 7-game series

I used basketball-reference.com to collect the outcome, head-to-head (H2H) results, total regular season wins, and playoff matchup results. They are as follows:

Notes: I started with 2003 because that is the first year the NBA expanded the first round series to 7 games. Lockout year win totals are converted based on win%. Seeds are corrected so that team with home-court advantage (HCA) is listed as 4, even if they were technically a 5 seed; this designation is more functional than the official seeding (e.g. doesn’t matter that a team is a division winner – they still didn’t have HCA). “H2H Cumul” is the outcome of the season series with a negative value indicating the 5 seed won more games. Wins comp is the difference between the teams for regular season wins.

Home-Court Advantage is Not Predictive of Series Outcome

The 5 seed has won more than half (17/32) of all 7-game 4/5 series in NBA history. This indicates that HCA generally has little or no predictive effect on the outcome of these series. That doesn’t mean it doesn’t matter, necessarily, but it’s safe to assume there are several other factors that are more important.

A response I’ve seen on Twitter is that the Blazers are 21-63 against the Jazz in Utah so the home-court advantage DEFINITELY matters in this particular matchup. Which is probably true, if you think games played between Billy Ray Bates and Darrell Griffith are somehow relevant to Damian Lillard and Donovan Mitchell.

Here’s a more relevant stat: during the Meyers Leonard era the Blazers have won 43 percent of their games played in Utah and 44 percent of their total road games. There’s no historical reason to believe that home-court is magically import relevant in a Blazers/Jazz series than any other 4/5 series.

Do head-to-head regular season games matter?

Of the 29 series that did not have a tied regular season h2h series, the h2h winner has prevailed has prevailed 62% of the time (18 of 29 series). That would suggest that the regular season matchup is possibly predictive of first round playoff success for 4/5 matchups.

In the three series in which the 4-seed and 5-seed have split the h2h regular season series, the 4-seed has won twice (Mavericks in 2005, Cavaliers in 2008) and the 5-seed has won once (Lakers in 2003).

Now the weird news: When the 4/5-seed have identical records the 5-seed is a perfect 6-0. When the teams have regular season records separated by two or fewer wins, the 5-seed is 13-4. When the teams are separated by three or more wins, the 4-seed is 11-4.

If the 4/5 seeds are evenly matched, as determined by regular season record, the 5-seed has historically been more likely to win.

What about another sweep?

The 4/5 matchup has only yielded four sweeps since 2003, and one of those was a 60-win Dallas team against a 49-win Memphis team. That series has the biggest regular season win disparity of any 4/5 matchup since at least 1984 (second highest is the 1995 SEA/LAL series with 9), and ultimately led to changes in playoff seeding rules. The 5-seed has never swept the 4-seed.

Miscellaneous

• Worst 4/5 upset probably belongs to the 1989 Atlanta Hawks who won 52 regular season games and held a 6-0 h2h advantage over the 49 win Bucks; the Bucks prevailed in 5 games. A 5-seeded Utah team also lost to San Antonio in 1994 after completing a 5-0 regular season h2h sweep.
• The west, as suspected, has been highly dominant since 2003, with western 5 seeds averaging 2.6 more wins per year than eastern 4 seeds.
• Last year the east’s 4-seed had more wins than the west’s — the Cavaliers with 50 and the Thunder with 48. That was the first time in 29 years(!) that the east has had a 4 seed with more wins than a western 4 seed.
• I originally wrote a similar article five years ago before the Blazers/Rockets 2014 series. Here’s a fun passage that came true:

For Blazers fans who want to take an optimistic approach, there is an odd trend that may give you hope. Previously, 4/5 seeds have finished with identical records only twice: 1) Denver/Utah in 2010, 2) Clippers/Memphis in 2013. In both these cases the teams had high win totals (53 and 56, respectively) and the 4 seed held a 3-1 h2h series victory; these stats very closely match this year’s Portland/Houston series. In both cases 2010 and 2013, the 5 seed pulled off the upset in 6 games.

I spent way too long making an interactive spreadsheet that allows you to fill in hypothetical outcomes for the remaining games and give you the seeding that would result. Click on it!:

Tl;dr: HCA is basically meaningless for 4/5 matchups, but h2h regular season records are somewhat predictive.