Defense has been bright spot for Boston in early part of season

The Celtics rate well in defensive metrics, but getting Marcus Smart healthy for an extended period of time would help Boston thrive. AP Photo/Pat Sullivan

The Boston Celtics will reach the quarter mark of the 2015-16 season during Monday's visit to the New Orleans Pelicans. It has been hard to get a firm read on a team that has won 11 games by an average of 16.9 points and lost nine others by an average of 10.1 points. Third-year coach Brad Stevens is still trying to determine the right combinations to get the most out of his talent-balanced roster, but he has still managed to mold Boston into a top-5 defense, which is going to give the Celtics a chance to compete most nights.

That defense has left computers bullish on Boston. The Celtics ranked seventh in ESPN’s Basketball Power Index entering Sunday’s action and are projected at 48.7 wins overall. Boston owned a 94.5 percent chance at making the playoffs despite currently sitting outside the playoff picture in an Eastern Conference that has less separation than Boston's roster.

Boston currently ranks third in the league in defensive efficiency while allowing 97.1 points per 100 possessions. Only the San Antonio Spurs (92.9) and Miami Heat (95) have been better, and it’s worth noting that, despite having an inconsistent offense that ranks 18th in the league with an offensive rating of 101.2, Boston scored 105 points against both San Antonio and Miami during the Celtics' current road trip. With pace adjusted, Boston posted offensive ratings of 109.4 against San Antonio and 114.1 against the Heat.

What does it all mean? These inconsistent Celtics are still a bit of a mystery, but it's safe to say the good has outweighed the bad. You can't help but wonder if this team will look the same in February, if for no other reason than to alleviate the frontcourt logjam that is making things difficult for Stevens. And Boston will most certainly benefit when Marcus Smart is healthy enough to return to the floor.

Here's five things you should know about the Celtics' first 20 games:

The offense isn't the same without Isaiah Thomas: Regardless of whether he's starting or coming off the bench, Boston's offense is more potent when Thomas is on the floor. In Thomas' 624 minutes of floor time this season, the Celtics own an offensive rating of 104.8. That number plummets to 94.4 when Thomas is off the court (the lowest number on the team for any individual player). It's no coincidence that Boston's second-unit offense carried the team last season when Thomas was coming off the bench and, at the moment, it's the first unit doing the heavy lifting with Thomas starting 17 of his 20 appearances this season. Notable: Of players who have appeared in at least 15 games this season, Thomas ranks eighth in the league in points per 48 minutes. The players ahead of him? A venerable MVP ballot: Stephen Curry, Russell Westbrook, Paul George, James Harden, Blake Griffin, LeBron James and Anthony Davis.

The defense isn't the same without Evan Turner: Wait, what? One of Boston's biggest strengths this season has been a versatile, second-unit defense that has negated the obvious dropoff in offensive efficiency with Thomas running with the first unit. The Celtics are able to utilize switch-heavy reserve lineups headlined by Turner, Jonas Jerebko and Kelly Olynyk (the three players with the best individual defensive ratings on the team this season). Boston's defensive rating with Turner on the court is 92.9 and balloons to 102.1 when he's on the bench. The league's player-tracking data even reflects well on Turner, who was holding opponents to 33.1 percent shooting (or 9.9 percent below those players' season averages) through 19 games. Those who watched Turner get burned by Manu Ginobili late in Saturday's narrow loss to the Spurs will scoff, but Turner's versatility has helped Boston's defense more often than not this season.

The Celtics are intriguing small but are overstocked with bigs: Injuries in the backcourt have left Boston thin on reliable depth and forced Stevens to employ more traditional lineups this season. Boston's second-half surge last season was aided in large part by small lineups that often featured Jae Crowder or Jerebko at the power forward spot. The Celtics had success going small during a fourth-quarter rally in San Antonio on Saturday, and it might encourage Stevens to go that way more often moving forward. The trouble is that Boston already doesn't have enough minutes for its bigs. Consider this: Boston's opening-night starting bigs were David Lee and Tyler Zeller. Lee is nursing a heel injury that, for now, eases the big-man crunch, but he has expressed a desire for more minutes (this despite the fact that Boston is notably better when he's on the bench). Zeller, meanwhile, has logged six DNPs recently.

Avery Bradley deserves All-Star consideration: The jumbled East might make it tough for Boston players to earn All-Star consideration, and Thomas is probably the most likely to earn a February trip to Toronto. That said, there's a case to be made for Bradley, who has been excellent since returning from a leg injury in early November. Over Boston's past 12 games, Bradley is averaging 19.3 points per game on 50.3 percent shooting overall, including 48.1 percent beyond the 3-point arc. Bradley's net rating in that 12-game span is plus-10.8 points per 100 possessions, the best on the team in that span. It's easy to forget that Bradley, Boston's longest-tenured player, is still only 25 years old and continues to develop his game.

Celtics need a healthy Smart: The Celtics have maintained their glitzy defensive numbers without Smart, but they simply aren't the same team without him. Smart's defensive tenacity is impossible to replace (even if the Bradley/Thomas duo has given Boston's first-unit offense a more consistent punch). Boston's backcourt is thin on depth, and Stevens has limited the minutes for rookies such as R.J. Hunter and Terry Rozier. Stevens has hinted that Smart will come off the bench initially upon his return, which will only add to that unit's defensive energy, and pairing him with Turner again will ease Smart's ball-handling responsibilities. If Boston's identity is ultimately going to be hustle and defense, then Smart is the poster child for the way Stevens wants his team to play.