The Boston Celtics have raced out to a 9-3 start in the 2024-25 campaign, and for the most part, they have looked like one of the best teams in the NBA, which is what many fans were expecting from them. Their start to the new season hasn't come without its hiccups, though, with the biggest of the bunch coming on Tuesday night, when they suffered a 117-116 loss at the hands of the Atlanta Hawks in their first NBA Cup matchup of the year.

Losing to the Hawks on its own is bad enough, but when you consider that Trae Young, Bogdan Bogdanovic, and De'Andre Hunter all didn't suit up for this one, it makes things even worse. And when looking at this game, in addition to the C's two other losses on the year to the Indiana Pacers and Golden State Warriors, it's clear that some concerning trends are developing on defense.

Is this nitpicky considering Boston has lost only three games this season by a combined total of 10 points? Yes, but when you are as good of a team as the Celtics are, these are issues that need to get ironed out if they intend on repeating as champions this season. Losses are bound to happen, but their lack of cohesion on the defensive end of the floor is quickly becoming a big problem.

What's wrong with the Celtics defense?

Boston Celtics head coach Joe Mazzulla watches from the sideline as they take on the Atlanta Hawks at TD Garden.
Mandatory Credit: David Butler II-Imagn Images

On the surface, Boston's defensive metrics don't really indicate there's any reason for concern. Their defensive rating of 109.4 is sixth best in the league, and their 110.3 points allowed per game is ninth in the league. On most nights, the Celtics are doing what we'd expect them to do, which is knock down a barrage of threes and play airtight defense.

In their losses, though, and even in wins, like their recent overtime thriller against the Brooklyn Nets, there have been some concerning issues that have flared up. Boston's problem certainly isn't scoring the ball, as they are averaging 119.8 points per game (which is fifth in the league), despite only shooting 45.4 percent from the floor (which is 21st in the league). For as good as the C's have been on that end of the floor, there's another gear they can reach once their collective shooting percentage improves, which it will.

The problem is defense. In each of their three losses, the Celtics have had no problem scoring the basketball in clutch minutes late in the fourth quarter. The problem has been getting stops. The Pacers, Warriors, and Hawks were effortlessly getting buckets against the C's late in these games, and they did so in their own unique way.

With Indiana, their fast-paced, high-flying offense consistently caught Boston off guard late in the fourth quarter and overtime, which helped them win even though the C's scored 135 points. Against Golden State, the Celtics gave Stephen Curry and Buddy Hield way too much space to operate off screens, and in their latest loss to Atlanta, they got dominated on the offensive glass, which allowed the Hawks to dominate the shot margin and win the game.

Considering how many great defenders the C's have at their disposal, and how great they were during their championship run last season, this has been a bit of a surprising development. Jrue Holiday and Derrick White are struggling to keep up with guards at the perimeter right now, and Boston's assortment of front court players have been unable to consistently rebound the ball when opposing offenses put even the slightest hint of pressure on them on the glass.

It's fair to wonder if a busy summer for guys like Jayson Tatum, Holiday, and White is having a negative impact on them right now. Holiday's three-point shooting has dropped from a career-high 42.9 percent to 36.7 percent this season, and he's seemed a step slow on defense at times. White has been Boston's second-most consistent offensive player behind Tatum, but he also has found himself as the center of too many defensive breakdowns as of late.

Holiday and White are consummate professionals, though, and they should be counted on to get their act together on defense sooner rather than later. Head coach Joe Mazzulla's ever-changing frontcourt rotation, which has seen Luke Kornet, Xavier Tillman Sr., and now Neemias Queta rotate as Al Horford's backup, certainly hasn't helped in pick-and-roll situations, and that's something the team will get more comfortable with as the season goes on.

Rebounding is always something that Boston has to make a big effort to do, especially since they don't really have an elite rebounder at their disposal, even when the currently injured Kristaps Porzingis is at their disposal. Tatum is really their best rebounder, but he's only averaging 7.5 boards per game right now, which is proving to be a bit of an issue. Jaylen Brown has taken a big step forward, as he's averaging 6.6 rebounds per game, but all five guys on the court need to be committed to rebounding in order for the C's to be successful.

The good news for the Celtics is that they are only 12 games into the new season, meaning they have ample time to figure things out. They also will get their best big man in Porzingis back at some point, and as we saw last season during his limited time in the NBA Finals, that should prove to make a huge difference.

Until then, though, there are several correctable problems that this team needs to hammer out, and you can bet this loss to the Hawks is going to serve as a wake-up call for them. The best teams need to get punched in the face every once in a while, so hopefully this defeat to Atlanta will be just what Boston needs to get their act together and clean up their work on the defensive end of the court.