Last week we kicked off this series with a brief overview of shooting efficiency and possession efficiency. Beginning this week we’ll dig deeper into the components of each to determine exactly how much they impact the game. Last week I made this statement:
...for any other number to have meaning, it must be related to points in some way. Without that context it doesn't have any meaning.
That’s exactly what we’re going to do, starting with the components of possession efficiency. As you might recall, the formula for possession efficiency in a given game is this:
Possession efficiency = ORB - TOV
The result of this formula measures the number of true shot attempts for a team in a single game relative to their possession total. So if a team had 96 possessions in a game and this formula resulted in -4 then their true shot attempt total would be 92.
Today we’re going to break down the first component of this formula: offensive rebounding.
How much can offensive rebounding impact a given game? To answer this question I used the basketball-reference.com Team Game Finder to make a list of every game from the 2015-16 NBA season sorted by ORB% (offensive rebound percentage).* After copying this list into a spreadsheet I measured the ORB% at various percentiles. The results are as follows:
95th percentile: 36.2
90th percentile: 33.3
80th percentile: 30
70th percentile: 27.5
60th percentile: 25.5
50th percentile (median): 23.3
40th percentile: 21.4
30th percentile: 19.1
20th percentile: 17.1
10th percentile: 14.3
Fifth percentile: 12
Minimum: 3 percent
So, the typical ORB% in a given game is 23.3. This gives us a baseline to work with. Any ORB% above 23.3 produces positive value, while anything below it produces negative value. Let’s consider an example.
On January 1, 2016, the Cleveland Cavaliers beat the Houston Rockets 91-77. In this game they had 47 offensive rebound opportunities. If they grabbed offensive rebounds at the league median rate (23.3) they would’ve ended up with 11 offensive rebounds. However, their ORB% for this game was 36.2, dead on the 95th percentile. This produced 17 offensive rebounds. In this case the difference between the 50th percentile and the 95th percentile was six offensive rebounds. Each offensive rebound produces an extra true shot attempt, and each true shot attempt is typically worth about 1.08 points. Therefore, we can say that the Cleveland Cavaliers produced about +6.5 points of value with their offensive rebounding in this game.
Of course, there are many variables at play here. The number of offensive rebound opportunities varies from game to game depending on pace and the number of missed shots. The value of a true shot attempt varies from team to team, and sometimes an offensive rebound can produce either a better or worse shot attempt than is typical for the team.
But the concept is what’s important. In a game with league average pace and rebounding opportunities, the spread between a replacement level offensive rebounding effort (ORB% of 12, fifth percentile) and an elite effort (ORB% of 36.2, 95th percentile) is between 11-12 points. That’s enough to make an otherwise average offense as efficient as either the 76ers or the Cavaliers for a day. That spread can increase or decrease depending on the number of rebound opportunities.
And this doesn’t just impact offense. The defense impacts this number just as much. Keep in mind that there are about 44 rebound opportunities up for grabs in a typical game on each end of the floor. An elite offensive rebounding effort combined with an elite defensive rebounding effort can help a team win even if they face a significant deficit in shooting efficiency.
Of course, most games the results are far closer to the median. But rebounding is nonetheless very important and has a big impact on each game. Last season the Cavaliers had a season average ORB% of 25.1 and an opponent ORB% of 21.5. That’s about +1.7 points of value produced per game all season long. To give that some context, it’s the same as the difference between the No. 10 offense of the Boston Celtics (offensive rating of 106.8) and the No. 21 offense of the Atlanta Hawks (offensive rating of 105.1).
Who was the most important player to the Cavaliers in this respect? While Kevin Love deserves a hat tip for his defensive rebounding efforts, the answer is clearly Tristan Thompson. He was No. 2 in the entire NBA in total offensive rebounds last season. His personal ORB% was 13.5 during the regular season and 16.6 during the postseason. In the series against the Atlanta Hawks his personal ORB% of 23.1 was higher than their team ORB% of 22.8. When he was on the floor he literally produced more offensive rebounds by himself than their entire team. Absolutely, completely and utterly ridiculous.
This wasn’t a fluke. Against Andre Drummond and the Detroit Pistons, his ORB% was 16.6 against their team ORB% of 18.4. Against Bismack Biyombo and the Toronto Raptors, his ORB% was 16.5 against their team ORB% of 17.6.
Only the Golden State Warriors were able to contain him, limiting him to an ORB% of just 13.3. How? During the regular season they scored 20.9 points per game on fast breaks while playing at a lightning pace. Their opponents could only muster 13.8 points per game on fast breaks, which means they had a +7.1 point margin in this aspect of the game. Given that their average scoring margin was +10.9 points per game, this was a very important part of their game plan.
Against the Cavaliers, they were forced to slow down that pace and rebound as a team, which limited them to 9.4 fast break points per game (LeBron James, destroyer of fast breaks, helped a lot in this regard as well). Cleveland, on the other hand, didn’t have to rebound as a team because the Warriors didn’t have anyone like Tristan Thompson. They scored 16.4 fast break points per game, which gave them a +7 point margin on the break. In other words, the Cavaliers would not be NBA Champions without Tristan Thompson.
Next week we’ll delve into the other component of possession efficiency: turnovers. Once again, please feel free to suggest topics for this series on Twitter (@EVR1022) or in the comments below, and thank you for reading.
* ORB% offensive rebound percentage is an estimate of the percentage of available offensive rebounds a player or team grabbed. It’s not perfectly accurate but it gets you very close.