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Possessions are an essential metric in basketball analysis, but there is no single agreed-upon method for counting them. The NBA defines a possession as a team having the ball, ending when there is a field goal attempt or the defensive team gains possession. The most common formula for estimating possessions is: (FGA – OR) + TO + (Y * FTA), where FGA = field goal attempts, OR = offensive rebounds, TO = turnovers, Y = a number between 0 and 1, and FTA = free throw attempts. Offensive rebounds are treated as continuing a possession rather than starting a new one, and not all free throws use up a possession. The average number of possessions can indicate a team's pace and be used to create advanced team stats.
| Characteristics | Values |
|---|---|
| Most common formula for estimating possessions | (FGA – OR) + TO + (Y * FTA) |
| Components of the formula | FGA = field goal attempts, OR = offensive rebounds, TO = turnovers, Y = some number between zero and 1, and FTA = free throw attempts |
| Why Y is included in the formula | We don't know how many possessions are used up by free throws |
| Y estimated by Oliver | 0.4 |
| Y estimated by John Hollinger in Pro Basketball Prospectus | 0.44 |
| Average points per possession across college basketball | 0.994 |
| Possession ending events | made shot, made free throw, rebound, or turnover |
| Rebound types | defensive rebound, offensive rebound, team rebound |
| Team rebounds | Credited to a team but not to any individual player |
| Possession calculation by basketball-reference.com | 0.5 * ((Tm FGA + 0.4 * Tm FTA – 1.07 * (Tm ORB / (Tm ORB + Opp DRB)) * (Tm FGA – Tm FG) + Tm TOV) + (Opp FGA + 0.4 * Opp FTA – 1.07 * (Opp ORB / (Opp ORB + Tm DRB)) * (Opp FGA – Opp FG) + Opp TOV)) |
| NBA's stats site possession calculation | (FGA + .44*FTA – ORB + TOV)/2 with totals from both teams included |
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What You'll Learn
Understanding the definition of possession
Possession is a fundamental concept in basketball analytics. It is defined by the NBA as "Section XVIII-Team Possession". A team is considered to be in possession when a player is holding, dribbling, or passing the ball. The possession ends when the defensive team gains possession or there is a field goal attempt.
However, this definition is not always clear-cut, as a field goal attempt does not always indicate the end of a possession. For instance, if there is a missed shot, and an offensive rebound, the possession continues. This is an important distinction because getting and preventing offensive rebounds are skills that vary from team to team, and including them in possession calculations allows for a more accurate assessment of a team's offensive and defensive abilities.
Possessions generally end with a made shot, a made free throw, a rebound, or a turnover. However, not all free throws result in the end of a possession. Technical foul shots and "AND 1"s, for example, do not end possessions. Research has shown that about 44% of free throws result in the end of a possession, so a 0.44 multiplier is often used in possession calculations.
The most common formula for estimating possessions is:
FGA – OR) + TO + (Y * FTA)
Where FGA = field goal attempts, OR = offensive rebounds, TO = turnovers, Y = a number between 0 and 1 (often taken to be 0.4 or 0.44), and FTA = free throw attempts.
By understanding the definition of possession and using this formula, analysts can gain valuable insights into a team's offensive and defensive efficiency.
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The importance of possessions in basketball analytics
Possession is a fundamental concept in basketball analytics, providing crucial insights into a team's performance and facilitating comparisons between different squads. While it is a basic concept, it is essential to understanding the game's intricacies and making informed strategic decisions.
At its core, a possession in basketball refers to a team's control of the ball, beginning when a player is holding, dribbling, or passing it. This control continues until the team loses possession, typically through a field goal attempt, a turnover, or the defensive team gaining control. Possessions are integral to evaluating a team's offensive and defensive capabilities, as they serve as a standard unit of measurement. By examining a team's performance per possession, analysts can assess their efficiency and effectiveness, accounting for differences in playing style and pace.
The calculation of possessions is not as straightforward as it may seem. While a basic understanding is widely applicable, the specific formula for estimating possessions can vary. The most common formula is (FGA – OR) + TO + (Y * FTA), where FGA represents field goal attempts, OR stands for offensive rebounds, TO denotes turnovers, and FTA refers to free throw attempts. The variable "Y" in this equation accounts for the proportion of free throws that result in possession changes, with estimates ranging from 0.4 to 0.44.
The treatment of offensive rebounds further complicates possession calculations. Offensive rebounds can extend possessions, and their inclusion ensures that each team's possessions can be reasonably assumed to be equal. However, not all rebounds are created equal; team rebounds, for instance, are credited to the team but not to individual players. Additionally, rebounds that go out of bounds can impact possession counts, especially when touched by the defence.
Despite the challenges in precisely defining and calculating possessions, they remain a critical component of basketball analytics. Possession-based metrics provide a more nuanced understanding of team and player performance, allowing for comparisons between teams with different playing styles and paces. By delving into possession-based analytics, coaches, analysts, and fans can gain deeper insights into the game, evaluate strategies, and make more informed decisions to improve their teams' performance.
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Estimating possessions: the most common formula
Possession is a fundamental metric in basketball analytics. While there is no universally accepted way to count possessions, the most common formula for estimating them is:
FGA – OR) + TO + (Y * FTA)
Here, FGA stands for field goal attempts, OR stands for offensive rebounds, TO stands for turnovers, Y is a number between zero and one, and FTA stands for free throw attempts.
The first term, FGA – OR, accounts for the fact that a possession can end with a shot that is not rebounded by the offense. An offensive rebound would extend the possession, so it is subtracted from the total field goal attempts.
The second term, TO, represents turnovers, which also end a possession.
The third term, Y * FTA, accounts for free throw attempts. Not all free throws take up a possession—for example, technical foul shots do not. Research has found that approximately 44% of all free throws take up possessions, so Y is often estimated to be 0.4 or 0.44.
By using this formula, analysts can gain a better understanding of a team's offensive and defensive capabilities. For instance, by adjusting the possession count to 100, we can calculate offensive and defensive efficiency numbers. This allows for a more standardized comparison of teams, as it assumes that two teams have almost the same number of possessions in a game.
It is important to note that most equations average the team's stats with their opponents' for a more accurate estimate. While this formula provides a good estimate of possessions, it does not account for all the nuances of the game, such as the impact of individual players' styles and skills on the team's pace.
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The impact of offensive rebounds on possession calculations
Offensive rebounds play a significant role in possession calculations in basketball. A possession in basketball typically ends with a made shot, a made free throw, a rebound, or a turnover. When a shot is missed, a rebound is credited to the player who retrieves the ball. If the offensive team retrieves the ball, it is called an offensive rebound, and the same possession continues. On the other hand, if the defending team gets the rebound, the possession ends, and the ball is given to the team that got the rebound.
Secondly, accounting for offensive rebounds helps ensure that each team's possessions are equal. By treating offensive rebounds as continuing the same possession rather than starting a new one, analysts can assume that each team will have an equal number of possessions in a game. This assumption simplifies calculations and comparisons of offensive and defensive efficiency.
Additionally, the formula used by basketball-reference.com to calculate possessions also includes offensive rebounds. The formula is 0.5 * ((Tm FGA + 0.4 * Tm FTA – 1.07 * (Tm ORB / (Tm ORB + Opp DRB)) * (Tm FGA – Tm FG) + Tm TOV) + (Opp FGA + 0.4 * Opp FTA – 1.07 * (Opp ORB / (Opp ORB + Tm DRB)) * (Opp FGA – Opp FG) + Opp TOV). This formula takes into account both a team's statistics and their opponent's statistics to provide a more accurate estimate.
While offensive rebounds are crucial in possession calculations, it is important to note that there is still no universally accepted way to count possessions in the NBA. The definitions and calculations of possessions vary across sources, and there are ongoing discussions about how to handle specific scenarios, such as end-of-period possessions or possessions starting with very little time left on the clock.
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How to calculate points per possession
Points per Possession (PPP) is a player evaluation metric that attempts to measure the number of points a player generates for each possession of the ball. It is a useful statistic because it is straightforward and self-explanatory. However, it can quickly lose interpretability with a few decimal places.
To calculate points per possession, we must first understand what constitutes a possession. A team is said to have a possession every time:
- A player attempts a field goal
- Misses a shot and does not get the offensive rebound
- Turns the ball over (some sources also add "turnovers that are assigned to teams" for a more precise calculation)
- Goes to the line for two or three shots and either makes the last shot or does not get the rebound of a missed last shot
It is important to note that not all free throws take up a possession. Technical foul shots and "AND 1"s do not count as possessions, while there might be more than two free throws on one possession. Research has determined that about 44% of all free throws take up possessions, so a 0.44 multiplier is used to accurately represent the amount of possession during total free throw attempts.
Once we have the number of possessions, we can calculate points per possession by dividing the total points by the total number of possessions. This can be done for individual players or for entire teams.
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Frequently asked questions
A possession is defined by the NBA as a team having possession of the ball when a player is holding, dribbling or passing the ball. Team possession ends when the defensive team gains possession or there is a field goal attempt.
Possession is an important metric for understanding basketball analytics. Pace, offensive efficiency, and defensive efficiency metrics are all based on possession calculations.
The most common formula for estimating possessions is: (FGA – OR) + TO + (Y * FTA), where FGA = field goal attempts, OR = offensive rebounds, TO = turnovers, Y = a number between zero and 1, and FTA = free throw attempts.
The value of 'Y' is between 0 and 1 because not all free throws end a possession. Research has determined that about 44% of all free throws take up possessions, so a common value for 'Y' is 0.44.
No, an offensive rebound does not generate a new possession. If a team grabs three offensive rebounds after three missed shots, it is counted as one possession.
