Over the last few seasons, NBA teams have shifted the personnel manning the power forward and center positions. At this point, few teams employ two traditional bigs who do not shoot three-pointers. Many teams don’t even play one in many of their lineups. Guys like PJ Tucker, Kevin Love, and Draymond Green now play important minutes for their teams at the center position. These players don’t weigh as much, aren’t as tall, and are more of a threat from the perimeter than centers of the past.
Over that same time period, the league has largely come to the conclusion that getting back on defense is more important than hitting the offensive glass. But in this new, smaller environment, perhaps it is time to revisit the question of how teams should be valuing the tradeoff between offensive rebounding and transition defense. In particular:
• Can these more mobile bigs crash the glass and get back on defense faster than the plodders of the past? And if so, should teams send two bigs to the glass because they’ll be able to get back in the play faster if they don’t get the offensive rebound? Or is that advantage obviated by the fact that defensive bigs might also be quicker and more effective running the floor in transition off a defensive rebound.
• Are teams more susceptible to giving up offensive rebounds because their bigs aren’t as tall or strong as they used to be?
• Has the increased skill of bigs pulled defending bigs so far away from the paint that they’re not as capable of dominating the glass due to positioning?
These are all complex questions that will vary on a case by case basis. The point is that several factors have changed in the last few years when it comes to offensive rebounding and transition defense.
Ben Falk’s new site Cleaning The Glass (you should really subscribe) logs how often teams allow the opposition to get out in transition, their defensive rating on those possessions, and splits between opponent transition frequency and efficiency off a defensive rebound and off a turnover.
The downside in crashing the offensive glass is when it results in a defensive rebound anyway. Crashing the glass shouldn’t affect transition frequency or efficiency off turnovers, so I used the transition stats from off opponent defensive rebounds rather than just overall transition stats.
Years ago, the teams began to place a far greater emphasis on transition defense over pursuing offensive rebounds. As a result, they sent far fewer players to crash the glass and offensive rebound percentage (OREB%) plummeted, a trend that has accelerated over the last couple of years.
In the early years of this offensive rebounding decline, teams did not run much more often off misses. Over the last two years however, the frequency of transition possessions off live rebounds has jumped significantly.
Teams are clearly putting a bigger emphasis on pushing the ball after a miss over the last two years, which makes sense. Although Offensive Rating in transition off a live ball rebound has been dropping, a transition opportunity off a live rebound (1.126 points per possession league wide average in 2017-18) remains much more valuable than a half court possession (0.926 points per possession league wide average in 2017-18).
As offensive rebounding has gotten worse than ever, that reduction would in theory correlate with better transition defense. Yet transition frequency off misses has increased in the last two years. While there was once a clear correlation between a team’s OREB% and how often their opponents ran off defensive rebounds, that correlation has dropped significantly over the last 3 years.
The average correlation between OREB% and opponents running off defensive rebounds over the last 3 seasons has been 0.14. The previous 7 seasons had an average correlation of 0.44. This difference indicates that offensive rebounding hasn’t been nearly as harmful to teams’ transition defense as it has been in the past, or perhaps not offensive rebounding is not the transition prophylactic it used to be .
Many factors could explain this change. Teams may have gotten more effective in choosing to either crash the glass or get back on defense. For instance, teams might be sending just one player to the glass, but coaches have done a better job of emphasizing the need to sprint back in transition Instead of hitting the glass. Perhaps defensive players are staying back to help their smaller bigs against strong offensive rebounding teams rather than running the floor when a shot goes up. Here is how individual teams have balanced transition defense off misses with offensive rebounding this season:
The Oklahoma City Thunder are by far the best team in preventing opponents from running off live ball rebounds, and they’re also a top 3 offensive rebounding team. The Thunder are an outlier, but they illustrate how balancing offensive rebounding and preventing transition opportunities does not appear to be as difficult as it used to be.
Perhaps with shifting dynamics in both personnel and strategy, teams should reevaluate their principles on offensive rebounding vs. transition defense. Maybe teams should be sending more players to the glass because those players are faster and more mobile changing ends than they were just 2 or 3 years ago. In 2013, Jenna Wiens et al. presented a fantastic paper on the tradeoffs between crashing the glass and getting back on defense at MIT’s Sloan Sports Analytics conference . Wiens and company concluded that in a generalized context, teams should crash the glass more often. A similar analysis today might illuminate how the tradeoffs of offensive rebounding have changed in the new NBA environment. Such a study with access to spatial tracking data is needed to draw firmer conclusions, but preliminary indications are that perhaps crashing the offensive boards should come back in style.
Written by Liam Doyle (@LiamDoyleNBA)