The Celtics already had a team meeting. What’s going on with Boston?

The Boston Celtics are supposed to contend for an NBA title this season. Gordon Hayward is back healthy. Kyrie Irving’s knee is cleared. Jaylen Brown and Jayson Tatum are another year older. But even all of those stars — plus Al Horford — don’t feel like enough.

The mundane state in Boston is all the more frustrating given the Milwaukee Bucks’ rise, which comes a season after landing a new coach and mere role players, and the Toronto Raptors’ ascension, following one of the luckiest star-for-star swap opportunities in recent memory.

The Celtics aren’t bad. In fact, their adjusted net rating, which estimates point differential per 100 possessions fixed for strength of schedule, suggests they’re the NBA’s fourth-best team. But at 18-13, their record matches the star-less Clippers, the Blazers, and trails the Pacers.

The team knows things aren’t flowing right. They had a “team discussion,” according to Marcus Morris, after a 13-point loss to the Bucks on Friday night, which Kyrie Irving elaborated on. “There’s obviously some selfish play going on out there,” he said.

So what gives?

Young players still on rookie-scale contracts can’t be expected to develop to a perfect curve. An up year can be followed by an immediate down season, and vice versa, as we’ve seen for both Donovan Mitchell and De’Aaron Fox, among other 20-somethings who we’ve changed opinions on quickly. It’s normal.

For the Celtics, unfortunately, both Tatum and Brown are having worse years than the one prior.

For Tatum, his season efficiency numbers are about what they were (just 1 percent worse shooting, 4 percent worse three-point shooting), but defensively, his numbers have fallen. His defensive box-plus-minus, which estimates points saved, is nearly a point per 100 possessions worse than it was a year ago, and it’s on that side of the ball where he hasn’t been as consistent. In a year many expected Tatum to take on a larger role, but he’s mostly flatlined, if not slowed a step.

For Brown, his numbers are down across the board. He’s shooting 6 percent worse from the field, 12 percent worse from three, and isn’t making nearly the defensive impact we’re accustomed to, either. It’s taking a toll on the team’s overall production.

And while the youths find their way, the team’s established wing star is trying to do the same. Hayward, just 26 games back from an injury that cost him an entire season, isn’t there yet. He’s defending well, but shooting just 41 percent from the field. He’s scoring the fewest points per game of his career aside from his rookie year, and getting to the free-throw line at his worst rate ever.

The once-stacked wing position is looking bleak for the Celtics.

Mentally, this team isn’t on the same page even if, as a unit, some numbers speak otherwise. Part of that may be the injuries — with a variety of key pieces all missing time — but according to Irving, there’s more.

“There’s obviously some selfish play going on out there,” Irving said, according to The Athletic’s Jay King. He claimed part of the blame for the Celtics’ isolations and fadeaways, which stick out to him, saying, “I literally can do anything I want out there at any time I want. But at the same time, it’s what can I do for my teammates to be more successful?”

However, what’s being perceived in the locker room doesn’t necessarily play out on paper. The team’s assist percentage is up by 2 percent from last season, and the Celtics rank No. 4 in the league in turnovers, improving by more than 1 percent from last year, too.

Maybe there’s frustration in Tatum’s long-range two frequency (he’s in the 95th percentile among forwards, per Cleaning The Glass)? Maybe there’s anger in Brown’s inability to make threes? They’re also both in the 36th and 37th percentiles, respectively, in terms of assist percentages for their positions, per CTG, and aren’t developing into reliable playmakers.

None of the Celtics problems are obvious, which has made their start to the 2018-19 season so frustrating. But it appears Irving may have an idea. And maybe this players’ meeting will set a new plan in motion.