Protecting the rim

Jared Wickerham

Going into this season one of the defensive areas of concern for the Celtics by many fans was whether they could 'defend the rim'. Many have asserted that the Celtics don't have a true 'rim protector' and that is the sort of big man that they are clamoring for Danny Ainge to acquire.

Looking at our front-court, it is understandable where this concern comes from. Our best big man is not only our youngest player, but also 'length challenged' at just barely over 6' 8". And our two tallest bigs, Faverani and Olynyk, are both NBA rookies. Neither of our two most experienced bigs, Bass or Humphries are very long. Basically, we have size, we have experience, and we have length - but we do not have all three in any one body.

However, the question has been put out there: Is this a real concern?

In another fan post, Eric Weiss put together a nice statistical summary of the Celtics for the first 20 games and one of the things he put out there was

"- 59% conversion allowed at basket - 10th best in league, 28.5 shots/game at basket - 4th worst in league"

and this analysis:

"... Despite having a predominantly undersized frontcourt rotation, Boston has been able to limit the conversion efficiency of opponents rather well close to the basket. The perimeter defense has also been stout in terms of limiting the damage done from beyond the three-point arc. Overall, this has led to an effective team defensive effort when it comes to defending the initial possession.

However, the team has also given up a significantly high volume of total shots at the basket, despite limiting the overall efficiency of the opponent on those shots."

I tend to agree with this analysis, however I thought it was worth taking a closer look. Just how well has the team 'protected the rim'?

Let me define what I mean by 'protecting the rim': To me, this is about limiting shots at the rim. Although the 59% conversion number cited up above by Eric is nice, it is still WAY WAY higher than the conversion number teams shoot away from the rim. So, far more important than how well team's convert at the rim, is how often they get to the rim. The last sentence in the quote from Eric is critical.

Protecting the rim is about limiting dunks, layups and tip-ins (put backs off offensive rebounds).

So, how have we done at limiting these?

Visibly, to the naked eye, this has varied tremendously depending on which of our units are out there. And it isn't really just the bigs that matter there. When opponents are able to drive past perimenter defenders to take a shot in close, forcing a big to help - the result is often a miss (big man defending a small) ... but then a weakside ORB & put-back because no one rotated to pick up the big's original man. So a big man can be playing perfect D, but he needs at least one of two others on the team to do their jobs to prevent that situation. Another aspect of protecting the rim involves transition defense - preventing easy layups in transition. This is actually more of a guard and wing function than big man issue.

One way to measure at how well a team is protecting the interior is by looking at statistics for opponent dunks, layups and tip-ins. In particular, just what share of opponent shots are happening right at the rim?

For the team, the Celtics opponents have attempted 1620 FGA against them. Of those 66, or 4.1% have been dunk attempts, 416 (25.7%) have been layups and 27(1.7%) have been tip attempts. Overall, about 31% of opponent FGA have been dunks, layups or tips. 'At Rim' if you will.

Now, the next question is: What does this mean? Is this bad? Is it good?

For comparison, opponents of the Pacers (#1 Defense in the NBA) have attempted 25% of their shots as dunks, lay-ups or tip-ins.

So that looks like we have a LOT of ground to cover to be as good as the Pacers at preventing access to the rim.

On the other hand, for the Spurs (the 2nd best defense in the NBA) the number is a kinda-average 30.1%. And for the 3rd best defense, the Bobcats (yes, the Bobcats) they are allowing lousy 33.6% of their opponent's shot attempts 'at rim'.

And bizarrely, on the other end of the spectrum, for the league-worst defense Brooklyn, the number is: 26.3%. For the second-worst defense, Utah, the percentage of at-rim attempts is: 27.4%

What the heck?

This all seems counter-intuitive!! The Jazz and the Nets are 'protecting the rim' almost as good as the Pacers - yet their defenses SUCK!

So what is this telling us? That 'at rim' defense doesn't matter? Well, not entirely. Only that there are other factors to defense.

The Pacers and Spurs also happen to be in the top-10 in suppressing opponent 3PT% (Pacrs are 4th, Spurs are 9th). Both teams and the Bobcats are also very, very good at defending jump shots in general, all holding their opponents to low overall FG% (43% or lower). Meanwhile, the Nets, for all their excellent 'rim protection' absolutely suck at defending the 3PT shot, letting their opponents hit on a ridiculous 40.3% of their threes! The Jazz are average at 3PT defense, but both teams allow opponents to shoot 46% overall and are getting killed from mid-long range.

(Aside: Wow - and people are blaming Pierce and KG for the Nets woes? That, to me sounds like a perimeter D problem.)

The net point of that is that you need to protect both the interior AND the 3PT line, kinda equally well, in the modern NBA. Having the length of Lopez and Garnett protecting the paint isn't doing the Nets any good if their wings don't run shooters off the line.

Okay, so, overall, it looks like the Celtics are indeed on the below average side of preventing access to the rim. However, they are able to make up for that by being the absolute best (so far) at suppressing 3PT shot conversion. They've got half the equation down.

If they could reduce their tendency to let opponents take shots at the rim, that, combined with their already stingy 3PT D might elevate their overall D significantly.

So we must, indeed, be in need of a long, shot-blocking big man, right?

Well, let's look into some detail. Who on our team is doing well at 'protecting the rim'?

Here are some opponent 'At Rim' attempt percentages for when various players have been on or off the floor. (Players listed in order of most minutes ON floor. Brooks and Bogans haven't played enough to make this worth measuring. Smaller numbers under 'ON' and 'NET' are better):

Player            ON      OFF     NET
Jeff Green 30.3 34.1 -3.8%
Avery Bradley 32.0 30.6 1.4
Brandon Bass 32.5 29.7 2.8
Jordan Crawford 30.8 32.5 -1.7
Gerald Wallace 31.7 31.2 0.5
Jared Sullinger 29.3 33.3 -4.0
Vitor Faverani 31.2 31.5 -0.3
Kelly Olynyk 33.0 30.6 2.4
Courtney Lee 32.5 30.9 1.6
Kris Humphries 30.9 31.5 -0.6
Phil Pressey 32.2 31.2 1.0

So this indicates that the Celtics as a team are giving up a lower share of attempts at the rim when guys like Green and Sullinger on the floor. (Yeah, I know - another stat that reaffirms that those two guys are by far our best overall players.) In fact, when both Green and Sully are on or off the floor, the numbers become:

Players          ON      OFF     NET
Green+Sully 28.7 38.0 -9.3%

That ON/OFF differential is frightening. Basically our interior defense is abysmmal when we don't have these two guys on the court. When they are both ON the floor, our protection of the interior is pretty good, better than average. When they are OFF, it is like an open candy store left unattended with a bus full of kids stopping out front.

To put this differential in 'real' terms, consider that our opponents take an average of 81 FGA per game against us. If Green and Sully were to play the whole game, only 23.2 shots would be 'at rim'. If they missed the whole game, 30.8 would be at the rim. That's a difference of 7.6 shots taken at 'at rim' completion percentage compared to much lower efficiency outside shots. That ends up being around a 5-6 point swing on the scoreboard.



Note also that Crawford's numbers are also very good. Now, some of that may be because he's been on the floor with Green and Sullinger a lot. But so has Avery and Brandon. Crawford may deserve a little more credit than folks give him on the defensive end, at least for helping prevent access to the interior.

Humphries numbers here don't surprise me. Watching him play, I personally think he is our best big man at defending the 'high paint' - the area just inside the free throw line, preventing interior passes and hedging the P&R. He's got very good footwork and active hands. His very low opponent lay-up attempt percentage of just 23.5% is indicative of that.

On the negative side of things, I hate to pick on him once again, but Courtney Lee's relatively high percentages here (compared to the other guards) is unfortunately indicative of his tendency to be late on help rotations - something that he got benched for last year. My subjective eye tells me he is doing better at that this year, but it is still a weak point. Courtney is an excellent on-man defender (with or without the ball), but he tends to get caught watching plays. Fortunately, his excellent shooting this year has outweighed this one defensive issue.



Kelly Olynyks' poor numbers also don't surprise me here. Beyond any issues with 'strength', or 'wing span', he's a rookie, learning a new system. He is getting caught making the occasional mistake.

The good news is that trends support overall team improvement in this aspect. The team has measurably been doing better in this regard as the season has progressed. Sullinger has been steadily playing more minutes, as have both Crawford and Humphries, and that's been a factor. I also expect as the team progresses and gains experience through the year that help rotations will be more responsive and quicker, reducing weak-side attacks on the rim.

Reducing turnovers on offense obviously would also help reduce transition layups and dunks. (*cough* *Rondo* *cough*)

Now, when Olynyk returns, it's possible that Humphries will see a decrease in minutes. And that could hurt in this one aspect of defense, at least in the short term

However, it is important to note that if Kelly returns to playing primarily with Sullinger and Green, that overall has been by far our most effective front court (net points per possession).

Futher, it has been not just their offensive efficiency (1.106 points per possession) that has resulted in their strong rating but in fact, their overall defense has also been excellent, with opponents scoring just .969 points per possession. That threesome has surrendered a bit more than team average in 'at rim' attempts (32.8%) but has made up for it by being very good at running-off 3PT shots, holding opponents to just 29.2% from beyond the arc and holding opponents to just 34.5% on mid-range shots.

This is just re-inforcing what we discussed up above, of course: That overall defense entails more than just 'protecting the rim'. Olynyk may be still a bit weak at helping protect the interior, but his length, defensive smarts and long step mobility are helping on the perimeter.

I don't know if this answers the question of whether we still need a 'big, long rim protector'.

Our best rim protectors, Sully and Green, aren't exactly long. They are, however, very skilled. And they both do not make very many mistakes with footwork , positioning and help rotations. Green's contributions are probably more in his ability to man up on the perimeter, preventing drives to the hoop. His long arms probably help prevent interior passes to cutters. And of course, Green obviously has shown he can chase down and help prevent transition buckets. Sully's ability to push opposing bigs around, disrupting their positioning is probably taking away post-up opportunities and obviously his superior rebounding is helping to take away ORB put-back opportunities.

Similarly, Humphries' advantages that are helping are more 'skill' than length and intimidation.

Overall, this tells me that while size is important, skill may be more important. Further, I don't want to buy more rim protection if it costs me too much on perimeter D.

Faverani and Olynyk both have size. Can they learn the defensive skills to become better in this area?

Or do we need to go out and get someone?

And is this ("rim protection") so important that it outweighs other factors in the game?

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