11 stats that explain how the Celtics became the NBA’s best team

Marcus Smart has an excellent assist/turnover ratio of 3.19/1.John Tlumacki/Globe Staff

The Celtics’ 21-5 start made some subsequent hiccups appear more alarming than they probably were. But the fact remains their 29-12 record at the season’s halfway mark leads the NBA. Here are some trends and statistics that explain how this team reached this point, and some that offer clues about what could still be cleaned up as the chase for a championship intensifies.

▪ Center Robert Williams started Monday’s game with Marcus Smart out. It’s unclear whether Williams will soon regain the spot for good, sending Derrick White to the bench, but White’s play could make coach Joe Mazzulla reluctant.

The Celtics have outscored opponents by 11.7 points per 100 possessions with White on the court this year, 3 points better than the next-closest rotation player. When White sits, the Celtics have a paltry plus-0.6 net rating, the team’s largest on/off differential.

▪ Speaking of on/off numbers, Jayson Tatum’s plus-9.0 is predictably sparkling. But fellow star forward Jaylen Brown’s numbers are puzzling. The Celtics have actually been 3 points per 100 possessions better with Brown on the bench, with a plus-5.6 rating when he is on the court and plus-8.6 when he is not.

Brown is averaging a career-high 3.1 turnovers per game and shooting a career-low 32.5 percent from the 3-point line. Interestingly, he has been dominant from closer range, making a career-best 58.9 percent of his 2-pointers, thanks in large part to an excellent mid-range pull-up.

Jaylen Brown is averaging 26.8 points per game this year.John Tlumacki/Globe Staff

▪ The last two seasons, Smart has loudly answered questions about whether he can be a floor general for a championship contender. He is the backbone of an offense that is finding open men and taking care of the ball. The Celtics’ 1.97/1 assist-to-turnover ratio leads the NBA, with Smart’s sitting at a career-best 3.19/1. Al Horford (4.32/1) and White (3.37/1) also deserve credit here.

The Celtics are turning the ball over on 13.4 percent of their possessions, fourth-best in the league. But they have truly soared in late-game clutch situations (when a game is within 5 points in the final five minutes), committing turnovers on just 8.9 percent of their possessions.

▪ Is this all too much math? Well, here’s an easy one to track. Horford is shooting 54.1 percent from the field and 50 percent from the 3-point line in wins, and 35.6 and 28.6 in losses.

▪ When the shot clock is running down, the Celtics are at their best attacking the basket rather than firing up long jumpers. With four seconds or fewer remaining on the shot clock, the Celtics are just 22.4 percent from the 3-point line, 26th in the NBA. But in these same situations, they’re making 48.6 percent of 2-pointers, ranking ninth.

▪ Coaches constantly preach about the importance of defending without fouling. The Celtics have done an excellent job of that. Opponents are taking .231 free throws per field goal attempt, the league’s second-lowest rate. Or, more simply, they’re attempting a league-low 20.9 foul shots per game.

After some shaky moments on defense to start the season, the Celtics are regaining their form at that end. Their 110.9 defensive rating ranks seventh, just 0.2 points outside the top five. Williams’s return and increased workload will likely boost these numbers soon.

▪ Tatum’s 3-point shooting has been inconsistent, but he thrives when he is in rhythm. He has made 41.1 percent of his 3-pointers on catch-and-shoot attempts; when he takes just one dribble, that figure plummets to 27 percent.

Horford has been Tatum’s most efficient quarterback. Tatum is shooting 46.8 percent from the 3-point line after receiving passes from the big man. He is below 40 percent with all other teammates.

Tatum celebrates after his game-sealing dunk against the Bulls Monday night at TD Garden.Jim Davis/Globe Staff

▪ The Celtics have regrouped since dropping a pair of early overtime games to the Cavaliers and turned into an excellent clutch team, with a 12-5 mark. There is still some room for improvement here, though. They are creating just 0.5 points off of turnovers in the clutch, ranking 29th. The good news is that opponents are attempting just 1.5 clutch free throws per game, the fewest in the league.

▪ The Celtics have an interesting shot profile. They run post-ups on 3.1 percent of their plays, 23rd-most in the NBA. But they’re scoring 1.09 points per possessions in these situations, tied for third-best. Similarly, they run handoffs on 3.2 percent of their possessions, 24th-most in the league, but are tied for third with 1.03 points per possessions on these plays. Handoffs will likely become more frequent with Williams back in the fold, too.

▪ The sample size is too small to read deeply into this, but the Celtics have seven lineups that have played 50 minutes or more. Six have positive net ratings, and the seventh, with Malcolm Brogdon joining the regular starters instead of White, has a ghastly minus-27.2. Brogdon has been an excellent sixth man, but he’ll probably stay there.

▪ Opponents are blocking just 3.7 shots per game, fewest in the league. This number is this low partly because the Celtics take 41.7 3-pointers per game, second-most, but it’s also an indicator of good ball movement.