|Andrew Lynch: Across Space and Time
40 Years of League Average-Adjusted Efficiency for Every Team
Defense wins championships. So does offense, but that’s not the cliche. It’s defense that
puts great teams over the top and turns the elite into the immortal. And the numbers
bear that out — in the last 10 years, every team that made the NBA Finals had an above
Not all championship defenses are created equal, however. Pop quiz! Which defense was
better: the 2011 Dallas Mavericks, or the 2013 Miami Heat?
A quick perusal of your favorite statistical website provides an easy answer. It’s the
Heat, of course! In 2013, Miami allowed 103.7 points per 100 possessions, via
Basketball-Reference; the 2011 Mavericks, on the other hand, had a defensive rating of
105.0. 103.7 is less than 105 (MATH!). The Heat win.
It’s not quite that simple, however. Each season is an entity unto itself, and a year-to-
year comparison can be a difficult prospect as a result. The further separated in time
the respective season, the more odious the task. There’s a litany of reasons for such
compartmentalization, but the commonality is change. Teams change across the board,
from rosters to ownership and everything in between. And the league changes, too.
Different rules come into vogue as others slip into history. Different points of emphases
take their place in any given year. Different strategies and tactics take route, as
defenses become more sophisticated and offenses adjust their shot selection and means
to such ends. Sum the variables and every season represents a different scoring
climate, where no two numbers are similar — no matter that they might be the same.
Back to those championship teams. In 2013, the average NBA team scored and allowed
105.8 pts per 100 possessions. In 2011, that number was significantly higher (107.3).
So was Miami really the better defensive team? Their raw defensive rating was lower,
sure, but it came in a league that was less conducive to the ball going through the rim.
Fortunately, we can use the average rating* in each year to figure out just how much
better each team was relative to the environment in which they played.
*Since everything sums to zero with 30 teams, the “average” team has the same
offensive and defensive ratings. Any references to “average rating” is this league
average for both offense and defense in the specified year.
Simple subtraction would get you one number, but a more accurate representation of
the distance from the middle of the pack would be a percentage. And that’s just as
easily calculated; we simply take the raw individual team defensive rating, divide it
by the league average for that specific year, and multiply the result by 100. The
product is a defensive efficiency number that’s adjusted to the league average for the
season in which the team played. It measures what percentage of the league average
scoring a team allowed; the lower the number, the better.
Take that 2013 Miami Heat team. They allowed teams to score 97.92% of the league
average points per 100 possessions. The 2011 Mavericks, conversely, gave up 97.86%
of the league average. The raw numbers, then, which indicated a clear advantage for
Miami, were misleading. When we account for the context of each season the 2011
Dallas Mavericks had a slightly better season defensively than the 2013 Heat did.
The same can be done for offense, too, of course, except in that case, the higher the
number, the better. In a nutshell, this is what I’m calling ORtg+ and DRtg+, shorthand
for “league-average normalized offensive/defensive rating.” It’s a concept that’s long
been around in baseball, and it’s existed in spreadsheets and APBRMetrics forum
threads for ages. But it’s generally not recognized on a larger scale, and I think that’s
largely because there is no searchable database for these numbers.
That problem is fixed. Basketball-Reference has offensive and defensive rating
numbers for each team going back to 1973-74, and they have the league average for
each season as well. I pulled all of that data to come up with ORtg+ and DRtg+
numbers for each team in each season going back that far. The spreadsheet is available
here; you can sort it by season, individual year/team combinations (i.e. the 2011-12
Charlotte Bobcats), franchise histories (sorry, Sonics fans, but the Sonics are labeled
“Thunder” here), raw offensive and defensive ratings, adjusted offensive and
defensive ratings, adjusted net rating (a simple subtraction of DRrtg+ from ORtg+),
teams that made the Finals, and parameters for the last 20 or last 10 completed NBA
Which is fun! The data in a spreadsheet is revealing in a lot of ways. But it doesn’t
quite do the scale of this project justice. Luckily for me, all-around blogging superstar
Ian Levy is a wunderkind with the visualization software Tableau, and he put together
this fun little chart:
Those dots represent the 1,073 individual team/season combinations in the dataset.
The y-axis is DRtg+; better defenses are to the bottom, worse defenses to the top. The
x-axis is ORtg+; better offenses to the right, worse offenses to the left. Quadrant IV, in
the lower right, is where all the best teams hang out — good defense, good offense. And
squares represent teams that made the NBA Finals.
The visualization is also sortable by Franchise, ranges of ORtg+ and DRtg+, individual
team/season combinations (tip: hover over the title bar in that checklist that says
“Specific Team and Season” to reveal a toolbar with a search option to more readily
find individual combinations — the format is “City Team – Year”), and specific seasons.
And they can be combined...CONTINUE READING AT HARDWOOD PAROXYSM