The objective of any defense is to prevent the team from scoring.  To this end, a defense can discourage high-percentage shots (shots at the basket), high-value shots (3-pointers and fouls), and create turnovers.  Quantifying defensive efforts, especially on an individual level, has long been an intriguing frontier of the basketball analytical world.

Preventing quality shots at the basket is important.  It’s why Hasheem Thabeet was drafted second overall.  It’s why teams use the 2-3 zone.  It’s why the 3-second rule exists.

So how do we grade this part of the game? Let’s start with blocks.  Blocks have traditionally stood as the measuring stick for paint defense but there are inherent problems with this using blocks as a proxy.  Not all blocks are recovered by the defensive team and thus, they offer opportunities for the offense to restart their offense and work a better shot.  The ego-fueled swat that sends the ball flying into the stands has in fact caused coaches to spew steam out of their ears.  And for good reason.  It’s probably best to just do this.

Another negative externality of the blocked shot is the fouling side effect.  The typical shooting foul will put about 1.5 points on the board.  This is the one of the many reasons why Thabeet was recently demoted to the D-League.  Among players who play 10 minutes a game, only two players fouled more than the UConn product.  After running a cost-benefit analysis, the Grizzlies decided he was better off playing for their JV team.  Sometimes, a block just isn’t worth it.

In the end, blocks do not correlate with good post defenses nearly as much as one would expect.  A superior way to measure basket defense is how well opponents shoot at the rim, or as we at Hoopdata.com have termed at rim field goal percentage.  This statistic captures not only a team’s shot-blocking ability but also their ability to alter shots by calculating how teams shoot on layups, dunks, and tip-ins.

The Boston Celtics, who rank fourth in at rim FG%, do not feature the shot-blocking prowess as some other teams but are much more effective at provoking missed shots around the basket.  Conversely, the Clippers have the second highest block rate in the NBA, thanks to the defected Marcus Camby, and yet find themselves 22nd in at rim field goal percentage.  The Celtics protect the basket far better than the Clips but you wouldn’t have guessed by only looking at their shot-blocking ability.

So let’s move away from blocked shots as a proxy for basket protection and focus more on at rim percentage.  I could offer a straight up leaderboard of opponent at rim percentage but I want to take this a step further.  Even at rim percentage can be misleading.  Why?  It still misses the foul component of basket defense as fouled shots are not included in field goal percentages.

Imagine if a coach told his players to foul every time the offense got an easy look at the basket.  It would probably work for a while but then the team’s best defenders would start fouling out by halftime and non-shooting fouls would earn a trip to the foul line sooner.   No coach would honestly advocate that strategy, but it appears that the Pacers have employed a version of it.  The Pacers have the third best at rim defense in the NBA as measured by at rim FG%.  However, they also foul their opponents a ton.  As a result, they have just an average defense when their at rim defense suggests they should be a defensive powerhouse.  Consider that the other leaders in opponent at rim FG% are Orlando, Chicago, Boston, and Cleveland– all excellent defenses.

To illustrate this dynamic, I plotted each team’s  opponent free throw rate (FTA/FGA) and their opponent at rim FG% below.  The text size and color gradient represents the portion of at rim attempts the team allows. The more you allow, the louder the data point.

Teams should strive to be in the lower left region, where opponents miss shots and don’t get to the line.  The Warriors, however, feature just about the worst combination of fouling and easy buckets, and likewise find themselves in the upper right region.

Orlando has an incredible post presence in Dwight Howard and at 4.1 fouls per 40 minutes, he fouls less often than the average center.  Perhaps the reason Dwight Howard isn’t getting the MVP recognition many believe he deserves is because he impacts the game in ways that the media can’t articulate.  Well here’s the evidence they’re missing.  The Magic protect the basket better than any other team in the NBA and they own the third best defense in the land.  He’s why.

It’s interesting that many analysts believe Brendan Haywood is the post presence that the Mavericks desperately needed when one considers that the Wizards allowed by far the highest at rim FG% in the NBA.   While they don’t give up a high percentage of shots from that area, they add to their post defense woes by fouling at a moderate rate.

The Bulls probably don’t garner the attention they deserve. They don’t foul, nor do they let opponents get any shots off at the rim.  They lost their best post defender in Tyrus Thomas but let’s not forget that he’s only played about a quarter of the teams minutes this season.  Joakim Noah has been superb on the defensive end this year but unfortunately for the Bulls, he’ll be out for the next three weeks with plantar fasciitis.   The Bulls hope they can hang onto a playoff spot without Thomas and Noah protecting the rim going forward.

As demonstrated here, teams like Indiana and Milwaukee have deflated opponent at rim percentages as a result of their fouling rates.  Others genuinely own the rim and create nightmares for their opponents without sending them to the charity stripe.  Keep this in mind as you watch the different defenses get prepped for their playoff run.