If Doc Rivers had one great concern about his team’s mindset heading into the year it was that they would take the wrong lesson from their postseason-turnaround. He feared that they would assume that everything would be fine once they got to April, because it worked last year.
The coach told anyone who would listen that the regular season was important and that the Celtics had to re-establish their in-season dominance. They had to be better at home and they had to close out games when they were there to be won.
After 10 games it appears that the message has been received. Not only are the Celtics 8-2, with two impressive wins over Miami and another over Oklahoma City, but they have also won three games in overtime and all four of their home games. Their two losses have come on the road in the second game of back-to-backs, which is perfectly reasonable and understandable, but Rivers still wants more.
“I would have taken it before the season,” Rivers said of his team’s record. “Having said that, I told our guys that we should be better, honestly. We’ve had a couple of really good games. We’ve also had some times where we’ve had the opportunity to close out games with stops and we haven’t done that. That’s where we’ve got to get better.”
That said, there are several positive signs -- and one note of caution -- for the Celtics beyond the play of Rajon Rondo who seems to be reinventing the art of passing on a nightly basis.
Here are five key statistical trends from the Celtics after 10 games:
IMPROVED REBOUNDING
Like most statistics, raw rebounding numbers don’t tell the whole story. Based on their total number of rebounds, the Celtics are about league-average on the boards, but dig a little deeper and it becomes apparent that they are well on their way to fixing what was their fatal flaw last season.
In any game the amount if rebounds will vary based on a number of factors that have nothing to do with controlling the glass. In a faster game there will be more shots and thus more misses and more boards to grab. The Celtics average about 91 possessions per game, which is on the slow side. Fewer possessions means fewer shots and fewer rebounds.
That’s where rebounding rate comes into play. Rather than look at the total number of rebounds, rebounding rate measures how effectively teams rebound based on the number of available boards.
By that measure the Celtics rank third in defensive rebounding, getting 77 percent of the available defensive rebounds. (The Bucks are a little bit better, while the Magic are far and away the best in the league at better than 81 percent). By comparison, the Celtics were right around league average last season, ranking 14th.
Paul Pierce has done solid work on the glass as has Shaquille O’Neal in limited minutes, but by far the biggest reason for this improvement has been Kevin Garnett who is getting more than nine defensive rebounds per game.
Garnett ranks third in the NBA in defensive rebound rate behind Reggie Evans, whose main job is rebounding, and Kevin Love who just pulled down 31 boards. Garnett has done more than cover for the loss of Kendrick Perkins. He has almost single-handedly turned the Celtics back into a defensive rebounding machine.
SHOOTING SMARTER, SHOOTING BETTER
The Celtics rank second in the NBA in field goal percentage at 49 percent, just a tick behind Atlanta. They are also fifth in 3-point percentage, making 41 percent of their shots.
The interesting thing for the Celtics is that they are taking noticeably fewer 3’s than they did last season when they averaged more than 17 attempts per night. This season they have taken only 13.4 per game, the lowest number in the league.
Where did those other 3’s go? Call it the Rasheed Wallace Corollary. Without Sheed clanging two out of every three bombs, their shooting percentages have gone up and they have become more efficient. 
They are also more selective about who gets to shoot from behind the arc. Pierce and Ray Allen have taken 97 of their 134 attempts from 3, while Nate Robinson (26) is the only other player who has taken more than five.
Robinson has struggled, although he seems to be coming out of his slump and there is hope that Delonte West will free him up to do what he does best. There have been no concerns with Pierce and Allen who are both shooting in the mid 40’s from 3-point range.
A big chunk of the credit for this improved shooting also goes to Rondo who allows them to play inside-out without the benefit of a true post-up presence. His ability to get in the lane and distribute close to the basket has allowed them to shoot over 65 percent at the rim according to Hoop Data, good for fifth in the NBA.
It’s no surprise that the Celtics also have highest percentage of assisted baskets from that range as well. That’s Rondo’s biggest impact.  
LIMITING TURNOVERS
It’s very simple for the Celtics. When they don’t turn the ball over they are exceptionally good on offense. When they do turn it over, they are very easy to stop.
They had an unsightly 54 turnovers in their first three games, but lately the trend has been improving. They had 61 in their last five games, which is just about where they need to be in order to be effective. Pierce has been better with the ball this season, but it’s been a team-wide effort.
The Celtics have always been a high turnover team (they are also among the league leaders in forcing turnovers), but if they can keep that number to a respectable level, they become almost impossible to guard in the halfcourt because of the balance they present to opposing defenses.
BIG THREE IN SYNC
The Celtics take about 80 shots a night and it stands to reason that you want your best players taking the majority of those shots. In Pierce, Garnett and Allen the Celtics have three players who shoot a high percentage with completely different offensive games and they are all finding room to operate.
They can win games when any of the three dominate the offense, but they are far better when they are all contributing and through 10 games they have achieved an almost perfect balance.
Pierce has taken 14.5 shots per game, Allen is at 14.4 and Garnett checks in with 13.3 attempts. That balance makes them very difficult to guard because defenses are forced to play them straight-up and all three have made a comfortable living feasting on single coverage.
Increasingly, you may see teams start to try to double-team Rondo to try to take the ball out of his hands. The Mavericks did that well last week (Sebastian Pruiti has a comprehensive video breakdown here).
The concern for the veteran stars, as well as Rondo, is that they are simply playing too many minutes. The three overtime games have skewed their minutes a bit, but as the season goes along Rivers needs to get more from his bench and lop about 3-5 minutes a night from each of their respective workloads.
NEEDED: MORE RESERVE HELP
For all the talk about how deep the Celtics are, the reality is that Rivers is playing with an eight-man rotation and only two of those bench players have had positive contributions so far this season.
Glen Davis has been fantastic, a legitimate sixth man and a game-changer off the bench who finishes games, while Marquis Daniels has been solid, doing a little bit of everything. But after that, things are unsteady.
Robinson has struggled, but he shot the ball well on the road trip and the Celtics are anxious to see him and West together. Semih Erden has shown flashes in limited minutes but he still has a long way to go.
Without Jermaine O’Neal and Kendrick Perkins, and with Shaquille O’Neal and Erden battling through various ailments, the Celtics are thin up front and it’s not likely to get better soon. Jermaine O’Neal may be out a couple of weeks, or it may be out longer. No one is really sure right now how bad his knee injury really is.
“Semih and Shaq are playing through whatever they’re playing through,” Rivers said. “Semih’s shoulder and Shaq’s everything, really. It’s a concern but there’s nothing we can do about it. We’re not going to go out and get anyone else. There are not a lot of really good 7-footers walking the earth that are not signed in the NBA, so we just have to make do.”
The Celtics have made out just fine through the first 10 games. They have proven, again, that their starting five is good enough to beat anyone in the league consistently. If they are going to maintain that level, however, the bench is going to need to be a bigger factor.