The Boston Celtics got off to a rough 0-2 start, losing star forward Gordon Hayward in the process, but then rattled off an incredible 16-straight wins to vault into first place in the Eastern Conference.
However, the team has been very inconsistent since then, and have currently lost three of their last four games.
In December, the Celtics are a mediocre 8-6 so far and haven't looked like the team that torched its competition in the first two months of the season.
So, what's wrong with the Celtics? And, can it be fixed? Coach Brad Stevens has his work cut out for him, but all is not lost just yet.
In fact, there are three reasons the Celtics have struggled lately, and one of those reasons will sort itself out over time.
As you can see below, the other two will require a bit more work, but are by no means unfixable. Here's a look at three big reasons the Celtics have been struggling lately:
They're getting crushed on the boards
In all of the Celtics' December losses, they've been out-rebounded, often by a significant margin. The only exception was a loss to the Bulls on Dec. 10, when both teams grabbed 52 boards.
Star forward Al Horford has never been an elite rebounder, but he does what he can on the boards. However, Marcus Morris's absence has been hampering the Celtics' rebounding ability more than anything else.
Morris returned for the Christmas Day loss to the Wizards, so having him back should help Boston turn things around on the glass.
They're worn out
As of Dec. 26, the Celtics had played 37 games - by far the most in the NBA. In fact, the next-closest teams to the Celtics in terms of games played only have 34 games under their belts.
Such a front-loaded schedule will become an advantage down the stretch as the Celtics have more rest in the second half of the season, but for now, it's wearing on Boston.
All of the Celtics' main rotation players besides Jayson Tatum, Terry Rozier and Aron Baynes have missed time already, and many of the banged up players simply need a bit more rest so they can return to their top form.
They're waiting for Kyrie Irving to play the hero
The Celtics' star point guard is playing at an incredible level this year, but even he can't do it all every single night.
Too often in late-game situations, the rest of the Celtics simply stand around and wait for Irving to make a play. That's a problem, because Irving's heroics usually work better when other players are moving around and creating stress for the defense.
Coach Brad Stevens is one of the best in the league at drawing up plays coming out of timeouts, but when things are happening in the flow of the game, the Celtics too often get stagnant on offense and simply wait to see what Irving is going to do with the ball in his hands.