Boston’s Jayson Tatum and Jaylen Brown are are both All-Stars this season.

First half summary: Only the Oklahoma City Thunder and Houston Rockets have seen bigger statistical drop-offs than the Boston Celtics, who have been 5.4 points per 100 possessions worse this season (+0.9) than they were last season (+6.3), when they were one of two teams that ranked in the top five in both offensive and defensive efficiency. Despite marked improvement from Jaylen Brown, the Celtics have taken big steps backward on both ends of the floor, and at one point, lost 14 of 21 games to fall to 15-17 on the season.

Kemba Walker missed the first 11 games and struggled to find a rhythm as he worked his way back from a knee injury. Marcus Smart, meanwhile, missed the last 18 games with a calf strain. But more consistent production from Walker helped the Celtics win four straight before the All-Star break. There are three teams standing alone at the top of the Eastern Conference, but the Celtics are slightly ahead of a large scrum of teams that has, like them, been hovering around .500.

Biggest question going into the second half: How good are they at their best? We have yet to see an in-rhythm Walker alongside a healthy Smart and the improved Brown. If Walker has found his offense and Smart’s return gives the defense a boost, the Celtics can fulfill their potential. But at their peak, they still might not be better than the fourth best team in the East. Their first game out of the All-Star break is in Brooklyn, and their last game before the trade deadline is in Milwaukee. So the Celtics, should they be at full strength, will have a pair of timely measuring-stick matchups. And if they don’t measure up, it will be fascinating to see if Danny Ainge, with a big trade exception burning a hole in his pocket, makes a move or stays patient.

Playoffs or lottery?: Health permitting, the Celtics should remain in the top six in the East and make their seventh straight trip to the postseason. But their four-year streak of reaching the conference semifinals could be in jeopardy. If Brooklyn, Milwaukee and Philadelphia are the top three seeds, we could have a scenario where the two teams that reached the conference finals last year — Boston and Miami — face each other in the first round.

The Celtics have a veteran core that can push them into the list of serious contenders. But a lack of depth is holding them back, especially if their top four perimeter players aren’t healthy throughout the second half of the season. Gordon Hayward’s departure is the biggest reason why they’ve taken a step backward, but it also left them with a tool (that trade exception) to help them move forward again.

— John Schuhmann