Celtics All-Star break roster evaluation: The starters and key reserves

When the Celtics have starters Jayson Tatum (left), Robert Williams, and Jaylen Brown, among others, they're easily handling opponents. It's just that they've only had their regular starting lineup in 23 of 60 games.Jim Davis/Globe Staff

Although the Celtics have hardly been perfect this season, their regular starting lineup is certainly not to blame for their inconsistency. The group consisting of Jayson Tatum, Jaylen Brown, Marcus Smart, Robert Williams, and Al Horford has been dominant.

In its 23 games together, that unit has outscored opponents by 26.5 points per 100 possessions. The issue is that the Celtics have played 60 games, so the lack of consistency within the starting group has been a hindrance.

If the team can stay mostly healthy over the final two months of the regular season, however, Boston could inch higher in the Eastern Conference standings. Here’s a look at those starters, and the team’s key reserves.

Jayson Tatum

It’s been an unusual season for the All-Star forward. His field-goal shooting percentages are at career lows. His 32.9 percent success rate from the 3-point line accounts for a stretch in which he somehow missed 20 long-range shots in a row. Despite coach Ime Udoka’s praise for his improved playmaking, Tatum’s assist numbers have dipped slightly since last year even though his playing time has increased slightly. On the other hand, opposing defenses are keying on him more than ever, and Tatum continues to make the right play time and again. He has emerged as a high-level defender, and his plus-9.6 net rating leads all of the regular rotation players.

Jaylen Brown

Brown had a few dominant performances at the start of the season, including his 46-point eruption in the opener against the Knicks, but he later missed 14 games because of a hamstring injury and took some time to regain his rhythm. There are times when Brown plays like a surefire All-Star and uses his athleticism to make other elite athletes look inferior. But at other times, his role within the offense appears clunky, and awkward turnovers pile up. Brown’s shooting numbers have taken a considerable dip this season, too. But he has attempted a career-high 4.9 free throws per game, an indicator that he is looking to attack the rim more. Also, Brown’s 101.1 defensive rating is tops among the regular rotation players.

Marcus Smart

Anyone who questions Smart’s value to this team should just look at the most fundamental indicator of success: the team’s record when he plays and when he does not. This season the Celtics are 31-19 with Smart in the lineup and 3-7 when he sits. He is fourth in the NBA in steals per game (1.8) and he conducts the league’s second-ranked defense. Smart has been determined to show Udoka that he can be this team’s starting point guard for years to come, and his role has some more clarity now that Dennis Schröder has been traded. It’s slightly concerning that Smart’s 3-point shooting numbers have dipped for three consecutive seasons after rising for three straight seasons prior to that.

Al Horford

Horford has said his lost year with the Thunder last season, when he was removed from the rotation so the team could focus on its younger players, was a blessing in disguise because it allowed him to focus on his body after years of wear and tear. And the 35-year-old big man has been reliable during his second turn with the Celtics. He’s averaging 10.1 points, 7.5 rebounds, and 3.4 assists while playing 28.3 minutes per game. During his last stint in Boston, he was the clear leader in the paint. Now, he’s willingly stepped aside for Robert Williams, who could be a rising star.

Robert Williams

Williams has been generating some defensive player of the year buzz recently. He’s averaging 2.2 blocked shots per game, tied for third in the league. And his ability to alter shots and even hold his ground after switching onto smaller guards has been impressive. On offense, he is a remarkably dependable lob threat. It seems that no matter how high or accurate the passes are, he finds a way to flush them through the hoop, usually with just one hand. His durability remains a concern, however. He’s been limited by a few nagging injuries this year while also playing a career-high 30 minutes per game, and ensuring that he is fully healthy for the postseason should be one of Boston’s top priorities.

Grant Williams

Williams has two primary responsibilities: Be able to reliably defend every position on the court on defense, and stand at the arc and be ready to fire up a 3-pointer when defenses collapse on Boston’s more talented players. He’s done both things quite well this season, and his 44.6 percent 3-point shooting has been one of the bigger surprises in the NBA.

Derrick White

White has played in just four games with the Celtics since being acquired from the Spurs Feb. 10. He’s fighting through a shooting slump, but the ball constantly moves when he plays. Boston is outscoring opponents by 26.9 points per 100 possessions when White is on the court. On defense, he and Smart have the potential to be a menacing pair.

Daniel Theis

Theis spent his first 3 ½ seasons in the NBA with the Celtics before being traded at last season’s deadline in a salary-clearing move. He was reacquired from the Rockets at the deadline this year. It was fair to question Boston’s willingness to take on his four-year, $36 million deal, which will have three years remaining after this. That’s a lot for a No. 3 big man who turns 30 in April. But there’s no question that his shooting and defensive versatility make him a much better fit than Enes Freedom. And if Horford or Robert Williams get hurt, Theis will be able to slide right in.