126: Rebounds and turnovers

Some thoughts on rebounds and turnovers through a Carolina blue lens.

How do basketball teams win games?

Years ago, Dean Oliver established the four factors of basketball success and the approximate weight assigned to each factor:

1. Shooting (40%)

2. Turnovers (25%)

3. Rebounding (20%)

4. Free Throws (15%)

These factors apply to both offense and defense. Among them, turnovers and rebounds can dramatically impact a team’s success.

Take North Carolina as an example.

Historically, Carolina dominated the offensive glass under head coach Roy Williams. This quantity over quality approach gave UNC more chances to score, or more whacks at the piñata.

Of course, teams gotta make shots to win. However, a team can often overcome poor shooting performances by generating more opportunities to score.

For instance, en route to the 2017 National Championship, North Carolina won three of its six NCAA Tournament games despite having a worse effective field goal percentage (eFG%) than their opponents.

Under Hubert Davis, Carolina’s style of play has changed. This doesn’t necessarily mean it’s better or worse. It’s simply different. UNC doesn’t emphasizes offensive rebounding to the same extent.

Let’s compare the two coaching tenures in terms of rebounds and turnovers.

And for a fair comparison, we’ll use the last four seasons of the Roy Williams era and the current tenure under Hubert Davis.

UNC is 90-38 under Hubert Davis, with a 70.3% win percentage over 128 games.
In contrast, Carolina was 87-48, or a 64.4% win percentage, over the last four seasons under Roy Williams (2017-18 through 2020-21).

What about their records in games where Carolina had a worse shooting performance than their opponent?

Using effective field goal percentage, here are the records for each coach when UNC recorded a lower eFG% than its opponent during this time span:

Coach          W   L   G  Win %
Hubert Davis  14  35  49   28.6
Roy Williams  22  41  63   34.9

UNC won ~35 percent of its games under Williams compared to 29 percent under Davis when shooting worse than its opponent. Of course, the sample size includes 14 more games under Williams than Davis.

Shot Volume Comparison

So, how has UNC changed its shot volume profile during this time frame?

As far as shot volume, we’re going to use John Gasaway’s shot volume index. Gasaway was kind enough to share a revised version with me a few seasons ago.

This version assigns a weight (.561) to avoiding turnovers versus gathering rebounds. The formula tries to calculate the number field goal attempts per 100 platonic possessions or possessions excluding free throw trips.

SVI = (100-(100*TO%))+(OR%*(0.561*(100-(100*TO%))))

Below is a table showing shot volume for the past eight seasons (offense, defense, and the delta between them) for Carolina:

| Season | Offense | Defense | Delta |
|--------|---------|---------|-------|
| 2018   | 100.8   | 95.7    | 5.1   |
| 2019   | 99.2    | 92.2    | 7.0   |
| 2020   | 98.1    | 95.4    | 2.7   |
| 2021   | 97.9    | 93.0    | 4.9   |
| 2022   | 98.6    | 96.9    | 1.7   |
| 2023   | 99.3    | 96.2    | 3.1   |
| 2024   | 101.8   | 96.5    | 5.3   |
| 2025   | 98.3    | 97.9    | 0.4   |  

This season, Carolina is allowing ~97.9 field goal attempts per 100 platonic possessions, the highest in the past eight seasons. Offensively, UNC is attempting 98.3 field goals per 100 possessions, the third-lowest in the same span. The result is a significant decline in their shot volume margin.

This lack of shot volume puts pressure on Carolina to outshoot their opponents and capitalize at the free-throw line.

Trends in Rebounding and Turnovers

A five-game rolling average of rebounding and turnover rates over the past eight seasons highlights the shift in styles.

The rebounding advantage has faded under Davis, but to be fair, it was astronomical at times under Williams.

While the both offensive and defensive turnover rates have declined under Davis, the defensive turnover rate has seen a recent uptick. Carolina continues to excel at avoiding turnovers offensively too.

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Rebounds and turnovers aren’t the only keys to success, but they often paint a clear picture of how a team needs to perform to win.

Under a new head coach and in an ever-evolving sport, changes in style and strategy are expected. But when the results don’t match expectations and the approach looks different, it brings questions.

Is the shift in strategy the issue? Or is it simply a matter of execution?

Tonight, UNC plays Wake Forest in a pivotal game that could shape the rest of their season. The Tar Heels have lost their last three games in Winston-Salem by an average of 15.3 points. To turn the tide, turnovers and rebounds will play a critical role.

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Thanks for reading this far, and hopefully you found this Carolina specific newsletter useful. If not, you can find college hoops data for all 364 D-I teams for the 2024-25 season here:

And as always, you can view the code for this post and other posts here.

Enjoy your Tuesday.