The Importance of Possession in Basketball Explained
Possession in basketball is one of the most fundamental concepts but still does a lot of the heavy lifting in the analytics world. In this article we want to help you understand possession at multiple different levels. From an intuitive explanation to statistical definitions, there are many ways to understand possession in basketball. And, from advanced metrics to efficiency measures, the concept of possession in basketball creeps in everywhere we look.
So let’s start at the beginning – where someone who was just learning the game would start – with an intuitive explanation of possession in basketball. As we move through the following sections, the concepts will get progressively more complex. So, for those coming in with some base basketball knowledge, feel free to skip ahead to the more advanced sections starting here.
To receive email updates when new articles are posted, use the subscription form below!
An Intuitive Explanation of Possession in Basketball
Basketball, like most sports, is a game based on taking turns. One team has the ball, then the other team does. Teams trade possessions back and forth until the game ends. On a team’s possession, they can dribble, pass, or shoot the ball.
The most important thing that can happen on an individual team’s possession in basketball is that they can score. The offense, the team possessing the ball, is trying to score while the defense is trying to prevent them from scoring. The more successful a team is on their offensive possessions, the more likely they are to win the game. Similarly, the more successful a team is on defense during the other team’s possessions, the more likely they are to win the game.
The more possessions on which a team is successful, the more likely they are to win the game. This seemingly trivial fact is actually at the heart of a significant amount of the advanced analytics that color the game of basketball.
How Possessions are Counted in Basketball
It seems like counting possessions in basketball should be straightforward and not really something that should be debated. However, counting possessions from box score statistics is actually kind of complicated. Click here to read our previous article about how to count possession in basketball.
In the NBA’s official possession counting statistic, possessions are estimated by looking at the box score. The formula, borrowed from the previous article I listed is here:
The main idea of this formula is that every possession either ends with a shot, a free throw attempt, or a turnover. However, not every shot, free throw attempt, or turnover attempt ends a possession. There are a few ways in which this can happen.
For example, if a team secures an offensive rebound, then their missed shot attempt didn’t end their possession. Therefore, subtracting offensive rebounds from field goal attempts corrects for this fact.
Free throws are weirder. Sometimes players get an and-1 or a one-and-one and only take one free throw before the possession ends. Sometimes a player is fouled on a three and gets three free throw attempts. The 0.44 factors is included in the above formula because on average every 0.44 free throw attempts lead to an ended possession.
While this formula is a good attempt, we can do a little bit better. Consider the following:
- Replacing 0.44FTA with actual free-throw line trips results in a more accurate measure of possessions in a basketball game
- Sometimes buzzer-beaters don’t actually result in the other team gaining possession.
- Sometimes a shot made with 1 second left which result in a half-court shot don’t lead to meaningful possessions
The most accurate way to count a possession in basketball is to “have a human in the loop” to make judgments for what actually constitutes a possession. In the next section, we’ll see why counting possessions is really important.
Offensive and Defensive Efficiency and Possessions
The reason that possessions in basketball are so valuable to talk about is that each team gets the same number of possessions. Consider the following formula that tells us how many points a team takes in a game. Points = (pts/possession) * (possessions) .
For each team, the number of possessions is the same. Therefore, in order to score more points than our opponent, we need to have a larger number of “points per possession”. This number is precisely what we call offensive and defensive efficiency. For an in depth look at efficiency in the NBA, check out our article here about pace and efficiency metrics.
The game of basketball isn’t about maximizing possessions, its about doing the most with the possessions you’re given. Because the number of possessions is a fixed commodity, every action in an NBA game has an opportunity cost. Taking an ill-advised long 2 might be more detrimental than you think because you’ve actually decreased your team’s offensive efficiency.
To put that another way, the mathematics and analytics tell us that basketball is all about passing up an OK shot for a good shot or passing up a good shot for a great shot.
The realization that basketball is all about efficiency led to many of the differences between the modern game and the game of our parents day. Here’s one example. Take a look at the second graphic in our old article about NBA shooting efficiency. The per-shot efficiency of three point shots is only matched by the per-shot efficiency of shots taken within 3 feet of the rim! This realization means that any time a long two or a jump shot is taken, we might be sacrificing efficiency which makes it harder to win the game.
This realization that basketball is all about efficiency also led to more widespread use of pick and roll offense in recent years. A pick and roll is one of the most high-efficiency ways to run a possession in basketball. A pick and roll play leading to an easy shot is more efficient than a long two-point jump shot. A team running more pick and roll will have a higher overall efficiency. This team will score more points and win more games.
Now that we’ve seen how possession in basketball analytics leads to discussions of efficiency, let’s look at how it enters into other advanced stats discussions.
Possession in Other Advanced Metrics
In the last section, we talked about how basketball is a game about efficiency when it comes to your possessions. Because of this, many advanced stats are based around the idea that all plays can be evaluated by either
- Gaining or losing possession, or
- Increasing or decreasing the efficiency of possessions.
Let’s see how this concept works in practice.
Valuing Plays via Basketball Possessions
An average offensive possession is worth about 1.1 points per possession. Therefore a steal or drawing an offensive foul can be seen as plays that add about 1.1 points of value to your team. This is because you’ve taken an opponents’ possession and, through your actions alone, have reduced the expected efficiency of your opponents’ possession from 1.1 points down to 0 points.
Note that this is one way to justify that certain players are better fits in certain systems. A player who gets a lot of steals will be more to a team allowing 1.2 points per possession than a team allowing 1.0 points per possession. This is a precise way of saying that good defenders make more of an impact when added to bad defenses! This same logic can apply to many other actions.
Player Efficiency Rating
One of the most popular NBA stats is player efficiency rating. Without our new understanding that basketball is all about per-possession efficiency, it makes natural sense to measure player quality via how efficient they are when handling the ball!
PER takes the concept of using possessions in basketball to create stats a step further than our steals example in the last section. We can assign value to nearly every different action a player can make. Drawing an offensive foul is worth 1.1 points in the same way that a steal is. Making a 2 or 3 point shot adds value by increasing the efficiency of your possessions. We can go on and on with rebounds, assists, etc.
But, at the heart of it all, PER leverages an understanding of the importance of possession in basketball to derive player value.
Plus/Minus Statistics
Plus/minus and its variants also exploit the importance of efficient possessions in basketball to explain player quality. Plus/minus counts how many more points your team scored than your opponent while you were on the floor. If, over the course of 5 possessions, we outscored our opponents by 3, then our plus minus total would be adjusted by +3.
At the end of the day, it doesn’t matter the total quantity of shots or rebounds or assists somebody makes, it matters how many more points we score on our possessions than our opponents do. Plus/minus focuses on this fact and measures player quality in this way. But, it all comes back to looking at possession efficiency.
Conclusions
Possession in basketball is one of the most fundamental concepts there is. But, it goes beyond simply understanding the rules of the game. Talking about possessions is at the core of many of the most advanced topics in the NBA. From efficiency ratings to plus minus stats, possessions do truly show up everywhere in the game.
To receive email updates when new articles are posted, use the subscription form below!
