Isolation Basketball: An Inefficient, yet Necessary Offense

It is the simplest play in the playbook. A player calls out: “Iso!” His other 4 teammates clear space for the player to go one on one against his defender in order to try to score a basket. Isolation basketball is a style that is popular among fans, allowing them to watch their favorite players go head to head and see who comes out on top. However, the role of isolation in the NBA is unique.

The Inefficiency of Isolation

Despite its popularity, isolation offense is not used to a great extent for the majority of NBA teams. Since the 2015-16 NBA Season (when isolation possessions were first tracked), only 10 teams have used isolations plays on over 10% of their offensive possessions. Given that there were 180 teams over this span, 5.6% of teams used isolations on over 10% of their offensive plays. Even though the average isolation possession only produced a meager 0.886 points over this span (the NBA average points per possession among all possessions for this span was 1.088, for reference), the teams that used isolation more frequently generally had a higher standardized offensive rating (standardizing offensive rating allows the values to be compared over time) than other teams.

Due to this, it may initially seem like utilizing isolation plays more frequently would lead to a more efficient offense. However, this is not necessarily true. The correlation between isolation frequency and offensive rating is heavily skewed by the outliers, which include all teams with an isolation frequency above 11.6%. The specific outliers were the Houston Rockets in 2019 (20.4% Isolation), the Rockets in 2020 (19.6%), the Rockets in 2018 (14.5%), and the Cleveland Cavaliers in 2017 (11.9%). Each of these teams was led by at least 2 all-stars: the Rockets from 2018 to 2019 had James Harden and Chris Paul and then in 2020 they traded Paul for Russell Westbrook, while the Cavaliers in 2017 had LeBron James and Kyrie Irving. Almost all the teams with a high isolation frequency and high offensive rating had 2 all-star caliber players: the 2017 Clippers (10.6% iso, z-score of 1.13) had Chris Paul and Blake Griffin, the 2018 Thunder (10.5% iso, z-score of 0.72) had Russell Westbrook and Paul George, and the 2021 Nets (9.9% iso, z-score of 1.46) have Kevin Durant, James Harden, and Kyrie Irving.

Teams without a duo of all-star caliber players, on the other hand, performed poorly when they relied heavily on isolation plays. These teams include the 2016 Lakers (10.6% iso, z-score of -1.55), who were led by Kobe Bryant in his final season (he was not good in his final season), and the 2017 Mavericks (10.5% iso, z-score of -1.08), whose leading scorer was Harrison Barnes. Therefore, we can see that isolation offense is not effective without one or two all-star level players. When a team cannot rely on all-stars to score in isolation, they are better off focusing their offensive possessions on set plays and more passing to get open looks.

One of the primary reasons that isolation offense is inefficient is because most players cannot score at a high enough rate to make these possessions efficient. Between 2016 and 2021, the average NBA points per all possessions was 1.088. Since 2016, there have been 219 players that have taken at least 100 isolation possessions. Of these 219 players, just 2 had an isolation efficiency above the NBA average points per all possessions. There two players were Chris Bosh (1.116 PPP) and Stephen Curry (1.098 PPP). Even players who are notable for their isolation play, like James Harden (1.084 PPP) and Kyrie Irving (1.039 PPP), are below the average NBA offensive rating when they use a possession for an isolation play. The reason for this is pretty simple: it is more difficult to shoot when going one on one with a defender since the shot taken will likely be contested or heavily contested, leading to fewer baskets made and thus a lower efficiency. Contrastingly, shots created by passing or screens are more likely to be easier to make since they will be less contested as defenders will have to rotate/switch to cover each player. This conclusion is supported by the data: the NBA average effective shooting percentage from 2016 to 2021 was 52.1%, but the average effective shooting percentage on isolation possessions was 47.3%.

This problem was also apparent for the 2021 regular season. The average isolation efficiency for players in 2021 was 0.927 points per possession, with a standard deviation of 0.139 points per possession. Since the NBA average efficiency was 1.117 PPP (according to NBA.com), the standardized value (z-score) required to make isolation offense an efficient play was 1.37. According to the Normal Distribution, only about 8.5% of players were expected to have a standardized score of at least 1.37. In the regular season, 79 players had at least 50 isolation possessions, but only 5 players scored above the average NBA efficiency when they ran isolation offense. These players were LaMelo Ball, DeMar DeRozan, Kevin Durant, Zach LaVine, and Steph Curry. That means that only 6.3% (very close to the expected 8.5%) of players that used isolation possessions fairly frequently were efficient enough to make isolation a good play. From this, we can see that only a select few players (about the top 8%) should try to run an isolation play against their opponent frequently, while the vast majority of players are better off attempting to initiate more passing and movement on offense if they are able to.

The Playoffs: A Whole New Game

The role of isolation basketball changes immensely in the NBA Playoffs. It is easily noticeable that more teams run isolation plays during the playoffs than in the regular season. During all but one postseason between 2016 and 2021, the frequency of isolation possessions increased by at least 2 percentage points. In several cases, teams ran isolation plays 1.5 times more frequently in the playoffs than in the regular season.

From the graph above, we can also see that there are differing trends in the usage of isolation in the regular season and playoffs. Teams have been using isolation offense at a decreasing rate during the regular season, with the frequency of isolation plays falling in every regular season since 2017. However, the playoffs show a different trend. Since 2019, the rate of isolation plays being run in the playoffs has increased after it fell from 2018 to 2019. Even though it may seem contradictory, there is a reason that teams choose to increase their isolation usage during the postseason.

In the postseason, running isolation becomes a better play. First off, the efficiency of isolation plays has increased during the postseason in every year since 2016. Meanwhile, the efficiency of non-isolation plays was usually either similar in the postseason and regular season or slightly higher in the regular season. The reason that isolation offense becomes more efficient for teams in the postseason is that the best isolation players use more of their possessions to go one on one with their defender. We can use this postseason as an example. Several high efficiency isolation players increased their isolation frequency in the playoffs, such as:

  • James Harden (88th percentile of iso efficiency), 33.6% (regular season frequency) -> 55.8% (playoffs frequency)
  • Damian Lillard (90th), 19.1% -> 25.9%
  • Giannis Antetokounmpo (85th), 17.8% -> 23.6%
  • Luka Doncic (80th), 16.7% -> 23.2%
  • Kevin Durant (94th), 14.1% -> 23.0%

On the other hand, several of the least efficient isolation players do not make the playoffs since their teams are not good enough. In 2021, this list includes players like John Wall, Brandon Ingram, De’Aaron Fox, Collin Sexton, and Karl-Anthony Towns. Because the high efficiency isolation players are increasing their frequency of isolation possessions while many low efficiency isolation players are not playing in the postseason, the overall average efficiency of isolation plays increases during the playoffs.

Another reason that isolation plays are more useful in the playoffs is because other efficient play types are not as available. Among the play types that decreased the most from the regular season to the playoffs in 2021 were spot up plays and transition plays. The decrease in the availability of transition opportunities is especially hurtful to offenses: transition shots had an effective shooting percentage of 60.8% in the regular season, far surpassing the NBA average of 53.8%. With fewer transition and spot up chances during the postseason, teams opted for more isolation possessions and pick and rolls. Additionally, having fewer transition possessions, which are very efficient possessions, brings down the average points per possession during the postseason, also allowing isolation plays to be more effective. Even though isolation plays may be very inefficient during the regular season, it is still important to run a few isolation plays per game because the practice would likely help in the playoffs, when isolation plays become much more valuable.

Conclusion

Isolation offense is usually an inefficient way to try to score, but sometimes it can be useful. Running more isolation when a team has a duo of all-star level players will likely lead to a better offense, since the players can score efficiently on their isolation possessions and because it will allow them to incorporate more variety in their offensive options. However, when a team does not have that level of talent, they are better off avoiding a high usage of isolation as it will likely lead to a worse offensive rating. In the playoffs, though, isolation becomes much more useful. Since transition and spot up possessions decrease in the playoffs, likely due to defenses actively trying to prevent them since they produce efficient scoring opportunities, isolation becomes much more prevalent in the playoffs. The efficiency of non-isolation plays goes down while the efficiency of isolation plays goes up, meaning that isolation is a better offensive option in the playoffs, especially if a team has a couple of all-star level players. Therefore, isolation offense has a valuable place in today’s NBA. Teams should continue to run isolation at a low rate during the regular season to allow them to gain practice for the playoffs, when they will have to use isolation much more often.

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