Methodology

Efficiency ratings

In basketball, not all points are created equal. A team that scores 110 points in 105 possessions is less efficient than a team that scores 100 points in 90 possessions. Efficiency ratings account for this by measuring scoring relative to the number of opportunities a team had, expressed as points per 100 possessions.

This is the foundation of pace-adjusted analytics. By removing pace as a variable, efficiency ratings allow meaningful comparisons between teams that play at different speeds and even in different historic eras.

Offensive rating (ORtg)

Offensive rating measures how many points a team (or player) scores per 100 possessions. A league-average offensive rating typically sits around 105-125 in the modern NBA (though in recent years this has been trending upwards). Teams above this average are generating points efficiently while teams below it are struggling to convert their opportunities into points.

Defensive rating (DRtg)

Defensive rating is the inverse of offensive rating. It measures how many points a team (or player) allows per 100 possessions. Unlike offensive rating, lower is better. A team with a defensive rating of 105 is giving up fewer points per opportunity than a team at 112, regardless of how many possessions each team plays. Defensive ratings typically range from 105-125.

Net rating (NRtg)

Net rating is simply offensive rating minus defensive rating. A positive net rating means a team is outscoring its opponents on a per-possession basis. Over the course of a season, net rating is one of the strongest indicators of team quality, often more reliable than win-loss record alone, as it captures how well a team is actually playing rather than how fortunate they have been in close games.

Terminology

It's important understand that efficiency ratings are often referred to by different names.

Offensive rating

• Offensive rating (ORtg)
• Offensive efficiency
• Points per 100 possessions

Defensive rating:

• Defensive rating (DRtg)
• Defensive efficiency
• Points allowed per 100 possessions

Net rating:

• Net rating (NRtg)
• Net efficiency

On Hoops Junkie we use "Offensive rating" or "ORtg" for short.

Player efficiency ratings

The same concept applies at the player level. A player's offensive and defensive ratings are derived from their team's performance during the possessions they are on the court. This means a player's ratings are inherently influenced by the teammates they share the floor with so in a single game sample it can be an unreliable indicator (much like raw plus-minus). However, over a larger season-long sample it can be a powerful indicator of a player's overall effectiveness.

Possession counting

The method we use to count possessions has a direct impact on efficiency ratings. The classic approach, pioneered by Dean Oliver, estimates possessions from box score totals using a formula that factors in field goal attempts, free throw attempts, offensive rebounds, and turnovers for both teams. The result is averaged across both teams to produce a single possession estimate for the game (commonly referred to as pace).

From the 2020-21 season onwards, we use a more precise method: counting possessions directly from the NBA's play-by-play data. Each event in the feed identifies which team has the ball, allowing us to track every change of possession exactly as it happens. For a deeper look at how we define and count possessions, see our possessions methodology.

At the team level, the difference between these two methods is relatively small. Dean Oliver's formula is a remarkably good approximation and the resulting team efficiency numbers are broadly similar regardless of which method is used.

The difference becomes far more significant at the player level. With the estimated approach, a player's possessions are typically derived from team totals, prorated by minutes played. This is a very loose approximation that assumes every minute on the court is equal, regardless of who else is in the lineup or how the team plays with that player.

With play-by-play derived possession counting, we know exactly which five players were on the court for each possession. This means a player's offensive and defensive ratings are calculated from the actual possessions they participated in, not a statistical estimate. The result is a much more accurate picture of individual efficiency.

Live team efficiency ratings

During a live game, efficiency ratings are normalised to the same per-100-possessions baseline used for end-of-game stats. This means the numbers you see mid-game are directly comparable to season averages and final game ratings.

For example, let's say it's midway through the first quarter. The Celtics have had 12 offensive possessions and scored 15 points, while the Knicks have had 11 offensive possessions and scored 9 points. To calculate each team's live offensive rating, we scale these numbers up to 100 possessions:

Celtics ORtg: 15 points ÷ 12 possessions × 100 = 125.0
Knicks ORtg: 9 points ÷ 11 possessions × 100 = 81.8

The same logic applies to defensive rating. From the Celtics' perspective, they have allowed 9 points on the Knicks' 11 offensive possessions, giving them a defensive rating of 9 ÷ 11 × 100 = 81.8. Their net rating at this point would be 125.0 - 81.8 = +43.2.

These numbers will naturally be more volatile early in a game when the sample is small. A single three-pointer in the first few possessions can swing a rating dramatically. As the game progresses and more possessions are played, the ratings settle and become increasingly meaningful.

Live player efficiency ratings

Player efficiency ratings follow the same normalisation approach, but are scoped to the possessions where that player was on the court. Continuing the example above, let's say Jayson Tatum has been on the court for 8 of the Celtics' 12 offensive possessions and the team scored 11 points during those 8 possessions. Tatum's live offensive rating would be:

Tatum ORtg: 11 points ÷ 8 possessions × 100 = 137.5

Meanwhile, during the 4 possessions Tatum was on the bench, the Celtics scored just 4 points. A teammate who subbed in for Tatum and played in only those 4 non-Tatum possessions would have an offensive rating of:

Teammate ORtg: 4 points ÷ 4 possessions × 100 = 100.0

The defensive side works the same way. If the Knicks scored 5 points during Tatum's 8 defensive possessions, his defensive rating would be 5 ÷ 8 × 100 = 62.5, giving him a net rating of 137.5 - 62.5 = +75.0.

Again, these numbers are volatile with small samples. Tatum's +75.0 net rating after 8 possessions is not a meaningful reflection of his ability. But by the end of the game, with 50+ possessions played, the ratings paint a much clearer picture of how the team performed with him on the court versus off it.

Up next: On/off differentials