Celtics' most important player is Al Horford, and that's a problem

The Boston Celtics are stacked on the perimeter, but they're relying on an undersized 32-year-old center to hold the team together.

Al Horford is the Celtics' engine, and his unique skill set defines Boston's identity on both ends. That became evident during last year's Cinderella playoff run, when Horford willed the team to within one game of the Finals despite the absences of Kyrie Irving and Gordon Hayward.

Horford led the effort to eliminate the Milwaukee Bucks with his 26 points in Game 7, he thoroughly outplayed Joel Embiid in the second round, and then bullied Kevin Love in the Eastern Conference finals. Irving and Hayward's perimeter skills are wonderful luxuries, but Horford's ability to guard all five positions while also stretching the floor and creating for his teammates is a necessity.

It's no coincidence that Boston's underwhelming performances this season have mirrored Horford's struggles. The veteran is averaging the fewest points, rebounds, and assists during his three-year run with the Celtics, which could all be tied to a nagging knee injury. Horford has sat out his team's last six games due to patellofemoral pain syndrome, and the Celtics have gone 3-3 over that stretch, including a 120-107 thrashing at the hands of the Bucks.

The Celtics called a team meeting to vent their frustrations after getting humbled at home on Friday night. Shoddy defense was undoubtedly part of that conversation.

Milwaukee rained hellfire beyond the arc with a smattering of unlikely threes from Tony Snell and Thon Maker. However, the Celtics ultimately crumpled because of their interior defense. The Bucks shot a perfect 8-for-8 in the restricted area in the fourth quarter, killing Boston's comeback hopes.

Horford's absence robbed the Celtics of their ability to protect the basket. He has twice as many blocks as any other rotation player on the team, so the Bucks decided to attack the basket in the fourth quarter.

Notice how Jaylen Brown tries to shade Malcolm Brogdon toward help during the play below, but nobody rotates over to the weak side to stop the easy layup. Horford would normally erase the shot, but his stand-in Daniel Theis just watched the play unfold.

Boston surrendered 22 baskets within the restricted area against the Bucks, a common trend during their last three losses. Phoenix and Detroit scored 22 and 21 restricted-area field goals, respectively, in their upset wins over the Celtics. Deandre Ayton recorded 23 points on 10-of-14 shooting, while Blake Griffin collected 27 points, and both of those assignments would have belonged to Horford.

Defending the interior is the lone weakness in Boston's otherwise impenetrable third-ranked defense. The Celtics rotate perfectly and smother the 3-point line, but they're vulnerable when an opposing player breaks the first line of defense. Horford is averaging a career high in blocks, and the Celtics are still a middle-of-the-pack team when protecting the rim. So without him, they're just hopeless.

The Celtics should rethink their reliance on Horford. After all, he's a 12-year vet with a mysterious knee injury set to keep him out indefinitely. Is that really a formula for success?

Horford hasn't even been at his best. He got worked by Serge Ibaka, Nikola Vucevic, Jusuf Nurkic, and even Noah Vonleh in some of the Celtics' losses this season. Those are matchups a healthy Horford should handle, but he's coming up short.

However, the Celtics lack viable alternatives. Aron Baynes is serviceable as a nimble banger in the post, but he's far too limited offensively to play extended minutes, and he's also out at least a month with a hand injury. Beyond him, the options are to play Marcus Morris as an undersized center, or rely on unproven prospects Robert Williams and Guerschon Yabusele. That's not exactly a Finals-caliber frontcourt rotation.

The solution would be to add frontcourt depth through a trade or via the buyout market. Anthony Davis is the pie-in-the-sky target, but adding him isn't permissible due to the obscure Rose Rule because Irving is on the roster. But even average players like Robin Lopez, Tristan Thompson, or Dewayne Dedmon could make a huge impact if the Celtics lure one of them away from their tanking situations.

Horford needs some backup to buy him rest and save his body for the playoffs, because the Celtics aren't going anywhere without him.