It partly has to do with defensive/offensive philosophy. On offense, after the shot goes up, Doc generally wants them running back on defense to prevent transition breaks. Boxing out try for offensive boards leaves you on the wrong side of your man if the miss caroms into their hands. Statistically, it will go into their hands almost 3/4 of the time anyway.
Percentages show that we have a better chance of getting the ball back from when it leaves our hands on the shot by getting back on defense, forcing a low percentage shot and then grabbing the _defensive_ rebound.
So that explains the lack of emphasis on offensive rebounds. On the defensive side, we are definitely supposed to be doing a better job. You have to be careful how you measure these things, though. If we force a team to take a lot of poor, low-percentage shots, then they naturally will have higher ORB counts - but it may not result in as large a rise in DRBs. The reason is you can have multiple ORBs per possession but only one DRB. Note also that giving up one or more ORBs on a possession is no guarantee they will score on that possession, but grabbing the DRB will guarantee that they wont.
What all that boils down to is that rebound counts are a suspect way to try to measure how well a team is rebounding. About the only measure I believe is useful is DRB% - which is the percentage of Defensive Rebound opportunities that you grab. All teams prioritize grabbing these, no matter what their defensive philosophy is and they have a distinct absolute game value (they stop a possession with zero points).
Here is an article I wrote a couple of years ago discussing how this Celtic team approaches rebounds. The numbers are a bit dated (they are for that year) but the concepts still apply to Doc (& Tom Thibodeau's) thinking:
http://www.celticsblog.com/2010/3/11/1368765/understanding-rebounds-and-theAs of the moment, the Celtics are ranked 20th in DRB%. That sounds bad, but you have to understand that teams are very closely bunched. The C's pull down 73.2% of Defensive Rebound opportunities. The league average is barely above that at 73.5%. The Lakers, with their twin towers, are barely above that, at 73.7% (16th).
Orlando, as is typical since they got Dwight, is #1 in DRB%, grabbing 76.2%. The Wizards are the worst at 69.2%.
In real terms if you make a team miss 60 shots, then the difference between the Magic and league-worst Wizards is that the Magic would grab 7 additional rebounds on defense.
So basically, right now, we are an 'average' rebounding team. I would like to see us get that number up to at least 75%. That would get us into the top 10 in DRB%.
I believe a lot of our rebounding problems are indeed due to lack of boxing out. Contrary to complaints, I believe JO is almost the only guy on the team who consistently boxes out well. Bass, Wilcox and, yes KG even, all tend to rely on their athleticism. For KG this still usually works. He's grabbing a very healthy 23.5% of DRBs. Some of that, he's been the beneficiary of JO's boxing out.
The good news is that this is something that can be coached and corrected. The bad news is we don't get many practice days in this schedule.
Topic: Why are the Celtics one of the worst teams at boxing out? (Read 7080 times)