There was a constant clamoring heard over the off-season, several variations on a theme:
". . . but if the Hoyas hope to return to the top of the Big East, they will need to do a better job on the boards."
Julian Vaughn will have to be a strong rebounder and hang on to the ball to get major minutes this year.
Jerelle Benimon can earn some minutes if he can play strong defense and grab some rebounds.
Let's take a look at each of these statements (I only made two of them up), one at a time.
Measuring Rebounding and It's Importance
Rebounding has been a
topic of great concern here, and
all over Hoya nation. But before I jump headlong into the charts and tables, I thought I'd review some of the basics we've covered here.
When we discuss rebounding, we like to talk about
rebounding percentages, rather than raw rebounding totals or the slighly more sophisticated
rebounding margin (tot. rebounds - opp. tot. rebounds).
Why? Let me re-post a brief explanation Alan provided
last season:
The most commonly used measure of rebounding is rebounding margin. There's a number of problems with this:
- Rebounding margin mixes offensive and defensive rebounding. Rebounding margin nets offensive and defensive rebounds for both teams, but the problem is that offensive and defensive rebounding are related, but different skill sets. Good offensive rebounding tends to be the result of strong individual effort. Defensive rebounding is much more of a team effort because it is much more highly dependent on all players establishing proper position. Good offensive rebounders often rely more on athleticism; defensive rebounders on position. More importantly, players rebounding on defense have positional advantage -- and rebounding margin doesn't account for that.
- Rebounding margin fails to compensate for differences in opportunity. There's an opportunity for a rebound on every missed shot. But not every possession ends on a missed shot. Some end on a made shot; some on a turnover. Since a team is more likely to get a defensive rebound than an offensive one, rebounding margin can make a team appear worse or better than it is simply because a team has more offensive opportunities than defensive or vice versa. For example, a team that forces a ton of turnovers will have less defensive rebounding opportunities and a lower rebounding margin than you'd expect. (Georgetown under Thompson would actually have an inflated rebounding margin over the years -- a negative turnover margin and better shooting than opponents means many more defensive rebounding opportunities).
- Rebounding margin fails to account for pace. More possessions means more opportunities for rebounds. This will not make a good rebounding team look poor, but a faster pace will make a good rebounding team look even better under rebounding margin.
A much better statistic is rebounding percentage. It is simply the number of rebounds a team gathers divided by their opportunities to grab a rebound. It is split into offensive and defensive rebounding percentage so as to avoid the problems of rebounding margin.
Last season, Georgetown's defensive efficiency slumped in conference, as the team finished the Big East regular season
allowing 1.03 points per possession, the most since 2004-5. This was often attributed to
poor defensive rebounding, allowing many second-chance points (think
Pitt or
St. John's).
Here are the team's defensive efficiencies and defensive rebounding percentages for the past five seasons:
Year D.Eff. Rank DReb% Rank
2004-5 105.2 8* 62.9 6*
2005-6 101.9 6 67.2 3
2006-7 97.3 4 63.1 13
2007-8 92.4 2 66.8 t-6
2008-9 103.1 7 63.2 12
*There were 12 teams in the Big East in 2004-5, 16 teams in the following seasons; all data from StatSheet.com
The Hoyas have only been among the league leaders in defensive rebounding once in the past five seasons, and that year (2005-6) was not a particularly strong defensive year. Indeed, while the team struggled to rebound defensively in 2006-7, the defense as a whole showed a strong improvement over the previous season, and the outstanding defensive team the next season were only middling defensive rebounders.
Of course, rebounding doesn't exist in a vacuum but is a component of overall team play. In fact, it is one component of what we call the
Four Factors, first named and described by Dean Oliver. Oliver hit open the concept when he realized that each possession will end one of four ways (here from the defensive perspective):
- a made field goal (opp. eFG%)
- a missed shot rebounded by the defense (D. Reb. %)
- a turnover (opp. TO Rate)
- a foul resulting in free throws (FT Rate)
If you account for these four factors when looking at a box score or season recap, you'll have a fairly good idea of what went well and what did not. Moreover, since rebounding is only a component of total team defense, some context must be considered when looking at rebounding percentages.
For example, Syracuse is normally a
mediocre to poor defensive rebounding team, averaging 63.5% Def. Reb. over the past five seasons while playing above-average defense in four of those five years. Of course, Jim Boeheim's squads primarily play a zone defense, which eschews strong defensive rebounding for low shooting percentages allowed and few fouls committed.
Let's return to the table above, but fill in all four of the factors for each season:
Year D.Eff. Rank DeFG% Rank DTO% Rank DReb% Rank FTRate Rank
2004-5 105.2 8 48.5 8 20.4 6 62.9 6 37.5 8
2005-6 101.9 6 48.9 9 19.3 7 67.2 3 26.4 4
2006-7 97.3 4 45.2 3 20.9 8 63.1 13 28.1 1
2007-8 92.4 2 41.8 1 20.3 7 66.8 t-6 39.8 12
2008-9 103.1 7 49.2 t-8 21.0 5 63.2 12 37.1 11
All data from StatSheet.com
Hopefully the first thing that jumps out is that the biggest driver of defensive efficiency is opponent's eFG% - if the other team isn't making shots, they're going to have a hard time scoring.
But we're here to talking about rebounding, so let's take a look at each season:
- 2004-5: The team was pedestrian across the board (remember, this was the old, 12-team Big East, so a ranking of 6 is just average). The one thing I did notice was that the league average defensive rebounding rate was only 63.2%, which seems especially low. Perhaps most of the teams in the old league favored zone?
- 2005-6: The Hoyas had an odd combination of strong defensive rebounding (a man-to-man trait) and few fouls committed (a zone trait). Along with the the poor shooting defense and few turnovers forced, this looks like a tall but defensively passive team (likely due to the short bench). Here, the strong rebounding was undoubtedly important - there is a substantial improvement defensively despite worse shooting defense and few turnovers forced.
- 2006-7: Georgetown's profile is very different here, much more like the zone-defense team that we discussed earlier. This team rebounded just as poorly as last year's club, but were able to ride their famous offense and an under-rated defense to the Final Four. This season shows clearly that, if a team defends shots well along with one other factor (here, committing very few fouls), that team can play stout defense - even if they give up a lot of second shots.
- 2007-8: And here, the lesson is simple - defend shooters better than any else has in the past five years, and everything else will just take care of itself. Obviously the Hoyas improved on the defensive glass, but that ridiculous shooting defense was the real story [UConn has the 2nd - 5th spots in def. eFG% over the past five years]. Indeed, in the infamous Davidson game, it wasn't the rebounding that failed the team, but a lack of turnovers and a complete inability to defend 2-pt FGs that doomed Georgetown in the second half. The pattern here - good rebounding, lots of fouls - smacks of a team playing mostly half-court man-to-man, and looks to have been a sharp change from 2006-7.
- 2008-9: Boy, the wheels sure came off that sucker. One reason I made sure to add rank next to each column is because the Big East's overall offensive (or defensive) efficiency varies from year-to-year: 2008-9 was the highest scoring in the past five seasons, at 1.041 points per possession, after 1.027 ppp the previous year. So despite the large uptick in def. efficiency, the Hoyas were actually better than average (or median) defensively in conference. The increase in forced turnovers and still high fouls indicates a bit more pressing by the defense, but the poor shooting defense was too big a handicap to overcome. If we compare last year to 2005-6 and call the differences in TO Rate and FT Rate a wash, the poor defensive rebounding last year looks to have cost the Hoyas about 1 point of defensive efficiency.
Is 1 point of defensive efficiency significant, especially when the typical spread in the conference is about 20 points? Well, it certainly could be when a team is seemingly winning most lopsided games but losing most close ones, and the Hoyas did in conference last season.
Returning to
a previous post on luck (as defined by the difference between actual and expected wins), we can actually just plug in that 1 point less defensive efficiency (about 0.6 points per game) and see what it's worth: ~0.4 wins. Not as much as you may have expected - if you want to round up and just call it one more win in conference play, would that have been enough to get the Hoyas on (or even over the bubble)? I'll leave that conjecture for others.
A quick bit on offensive rebounding
Throughout the discussion above, I've been entirely concerned with defensive rebounding. As
Alan noted in the section I co-opted from him, offensive and defensive rebounding rates don't necessarily correlate, since they depend upon complementary, not identical, skills and in part on the head coach's game strategy.
How have the Hoyas rebounded offensively the past five seasons?
Year DReb% Rank OReb% Rank TReb% Rank
2004-5 62.9 6 33.5 9 48.2 9
2005-6 67.2 3 38.1 4 52.7 4
2006-7 63.1 13 41.3 2 52.2 4
2007-8 66.8 t-6 31.7 12 49.3 12
2008-9 63.2 12 33.7 12 48.5 t-13
all data from StatSheet.com
Georgetown's best offensive rebounding season (2006-7) was also one of their worst for defensive rebounding. More to the point, despite losing 7'2"
Roy Hibbert, 6' 9"
Vernon Macklin and 6' 8"
Patrick Ewing Jr., last season's team - while no great shakes - actually was
a better offensive rebounding club that the 2007-8 team.
I've also included
total rebounding percentage [= (OReb% + DReb%)/2] in the table, and this final stat likely jibes better with common perception. Georgetown was not historically bad in either offensive or defensive rebounding last season, but by performing poorly in both
the team's total rebounding rate ranked as low as any JTIII-team.
I do wonder though, if the two strong rebounding seasons (Hibbert's sophomore and junior years) may eventually prove the aberration for the 21st-century Hoyas.
Julian Vaughn will be asked to shore up the Hoyas' meager rebounding this season. To understand whether he can help, we'll need to ask how well has Vaughn rebounded in the past, who will he replace, and can we expect an improvement season-over-season.
How well has Julian Vaughn rebounded his first two seasons?
Year %Min OReb% DReb%
Frosh 29.6 10.8 10.2
Soph 21.5 11.1 10.2
I don't have access to conf. only stats for Julian his freshman year at Florida St., so I'll be using full season stats in this section.
Okay, we have some numbers, but can we give them some context? Thankfully, Ken Pomeroy
has provided us with a very handy chart, showing average rebounding percentage as a function of height for all college players (
click on any figure to enlarge):
Julian Vaughn's height is
listed as 6'9" by Georgetown (he was
listed at 6'10" at Florida St. [
.pdf], so either he is shrinking or the Seminoles may be cooking the books). For the average 6'9" Div. I player, we'd expect an OReb% = 9.3 and a DReb% = 16.5.
From the chart, Vaughn is an above average offensive rebounder, but a suprisingly below-par defensive rebounder. In fact, in each of his first two campaigns, Vaughn was more likely to get an offensive rebound than a defensive one.
Who will Vaughn be replacing?
The primary additional minutes Vaughn will get this year were used by
DaJuan Summers last season. To put this bluntly, those minutes will not be hard to replace, at least from a rebounding perspective. Summers' number last season (OReb% = 5.5, DReb% = 11.7) were underwhelming, both as the nominal power forward for the Hoyas, and as a 6'8" college player.
Vaughn looks to have the skill set to greatly improve Georgetown's offensive rebounding this year, but probably won't be able to help much on the defensive glass outside of
Greg Monroe (OReb% = 9.0, DReb% = 16.6).
When Vaughn isn't on the floor this year, he'll likely be subbed for by
Henry Sims (OReb% = 7.0, DReb% = 12.7), who represents an incremental upgrade from Summers, but not much more.
Will Vaughn be a better rebounder this year?
This seems to be the most intuitive step that I've not addressed - as players get older and stronger, they should be able to out-compete younger players for rebounds, and therefore we'd expect a returning player (e.g. Julian Vaughn) to likely be a better rebounder this year.
That assumption is easy enough to check. Below I've plotted year-over-year defensive and offensive rebounding stats for Big East players from 2005-2008:
A quick explanation
- The x-axis is a player's rebounding rate for a given season, while the y-axis is that player's rebounding rate the following season.
- The markers are sized by player's % minutes played (>10% minutes both years to qualify) and colored by player height.
- The black line is a linear fit to the data, weighted by player minutes.
- The gray lines are the 95% prediction bands - 95% of the markers should be within these lines.
- The blue line is the 1:1 line - players that fall along the line performed at the same level both seasons.
The takeaways here are several: the fitted line of defensive rebounding is above the 1:1 line up to about
16%, indicating that
defensive rebounders tend to improve year-over-year up to about this point. But
the difference from year-to-year is very small, certainly less than 1% change on average. For offensive rebounding, the fitted is
below the 1:1 line above about 5%, which implies that those
players who are strong offensive rebounders (>5%) do not, in fact, improve from one year to the next. Most importantly, the majority of the data is well-scattered about the 1:1 line, especially defensive rebounding. Therefore, most of the change from one year to the next is just statistical noise, and that
players, on average, rebound at the same level each season. That is, rebounding ability (or desire) is fully formed when the players arrive in the Big East from high school.
So the results are mixed for Julian Vaughn. Statistically, if there's any change we'd expect a small improvement in defensive rebounding and a small decline in offensive rebounding.
More likely, what we've previously seen from Vaughn (and Sims) just may be what we can hope for during this season.
Can
Jerrelle Benimon help?
A complete unknown coming into this season is
Jerrelle Benimon, a player few are expecting to contribute significant minutes this year. Could Benimon be some sort of stealth rebounding freak? Possibly, but we have no way of knowing right now, and no mention of such prowess was made
during Kenner League.
What we do know is that he is 6'7" and 242 lbs. From Ken Pomeroy's chart above, we can see that 6' 7" players are part of the upper plateau for defensive rebounding, on average garnering 15.3% of defensive rebounds. So Benimon certainly has the right body-type for rebounding.
But, as we saw near the top, defensive rebounding can be an overvalued stat for overall team defense, and I'd like to see his full skill set before I suggest he should be taking minutes from Vaughn or Sims.
