The reeling Boston Celtics are struggling at league-low levels with Kevin Garnett off the floor

On Christmas day, the Boston Celtics absolutely and utterly waxed the Brooklyn Nets in full view of a national TV audience and the Nets’ home crowd. Playing an energetic style of ball, the C’s took Brooklyn out of their offense, only ceding buckets to random hustle plays from Gerald Wallace. Because the NBA’s unofficial start usually comes on Dec. 25, the prevailing joke was that the Celtics – at 14-13 following the impressive win – had decided to finally start their 2012-13 season.

As you probably know, things have more or less gone to rot in the week and a half since. Despite only playing four games in nine days because of a coast-to-coast-and-back schedule, the Celtics have lost four straight. Not only that, they’ve lost the four contests by an average mark of 19.8 points per game. Championship contenders usually don’t string two blowout losses in a row during the course of a season, much less four, and the Celtics are losing in ways that don’t remind of the respective low points during the 2009-10 campaign (one that saw them rally and make it the seventh game of the Finals) or last season (when they had a 3-2 lead in the conference finals).

Former Celtics guard and current Memphis Grizzlies stopper Tony Allen thinks he has the answer. And it may include, shockingly, Tony Allen:

Ben Rohrbach at WEEI, if you’re at work and don’t want to pull up the video, has the transcription:

“They’re missing a lot of pieces,” said Allen, who left Boston for a three-year deal in Memphis two summers ago.

Somewhat offering his stamp of approval on the replacement of Ray Allen‘s 3-point shooting prowess with fellow veteran Jason Terry, Allen instead harped on the absence of players … well … like himself.

“I don’t think they’ve really got a defensive-minded guy yet,” added Allen. “I mean, they’ve got one [Avery Bradley], but I can’t say he’s 100 percent just yet. I don’t think they’ve got the center like Perk [Kendrick Perkins]. It’s kind of hard finding a guy like — a guy who clogs up the paint, talks trash to you and can actually back it up. They’re just missing a lot. I don’t know. I don’t see the same team from 2008.”

It’s revisionist history, the easiest AP course you can take, but Allen might be onto something here. Game 7 of the 2010 NBA Finals could have swung in several directions – had Kobe Bryant taken better shots that night the Lakers may have won the contest in a walk – but a late game offensive rebound from Pau Gasol helped seal Los Angeles’ latest championship. Kendrick Perkins, after suffering an ACL tear in Game 6, could only watch helplessly from the sidelines. He could have been the difference, and the Celtics haven’t made it that far since.

Of course, the only thing that kept the Celtics out of last June’s Finals was LeBron James “getting it” in time for Games 6 and 7 and turning his career around on Boston’s dime. And Perkins has been roundly criticized for his play in Oklahoma City since the Celtics traded him to OKC in Feb. of 2011. The Celtics did lead the NBA in defensive efficiency last year working with basically the same cast of characters plus a noted sieve in Ray Allen.

For whatever reason, they’ve slunked to 13th in 2012-13, and at times it appears that the team’s only crime is its inability to play Kevin Garnett for 48 minutes a contest.

With KG on the floor the Celtics boast far and away the best statistical defense in the NBA. Without him, they’re below even the worst (the Charlotte Bobcats) the NBA has to offer. That sort of drop-off is obvious even before you see the stats, and just take in the eye test with Garnett – the dude is everywhere, and he does everything. Not only does he call out the other team’s plays, but his presence is felt on both the strong and weak sides in ways that can’t be described in the usual (“ball-hawking,” “shot-blocking”) terms. He’s a 7-footer with a massive wingspan and significant smarts that just seems to be in the perfect place every time down court.

Save for the 18.8 minutes a game he’s not on the court.

As Comcast’s Jessica Camerato notes, Garnett’s teammates are well aware of their failings in the post-KG landscape. From her gamer after the team’s most recent loss, Rajon Rondo speaks to the deficiency:

"We're not playing it (defense)," the point guard said following the Celtics loss to the Memphis Grizzlies on Wednesday. "I don't know (why). We've just got to try to take it one step at a time. It starts with me so I've just got to hold myself more accountable."

Not only is the drop-off without Garnett troubling in statistical terms, the idea that a unit featuring Rondo and various other Boston helpers would rank as the worst defensive team in the NBA without KG just makes no sense. Brandon Bass can’t defend and doesn’t have helping instincts, and Rondo’s quickness and long arms don’t really help much in an NBA that has made it nearly impossible for point guards to act as reasonable defenders … but worst in the NBA?

The light at the end of this mediocre tunnel comes with the idea that, in a playoff series, Garnett can ramp up to the 36.9 minutes per game he played in last year’s postseason run. That six months of saving his legs could ease the Celtics into one last two month stretch to the Finals. That a team built for the postseason could finally get the chance to act as it should during the time of year it was bred for.

Boston, percentage points behind the eighth-seeded Philadelphia 76ers, is out of the playoffs right now. And while Avery Bradley’s return has warmed the ruddy hearts of the C’s faithful, the Sixers could possibly add an All-Star starting level center at some point between now and the end of the regular season. There’s always the real chance that Andrew Bynum’s return could set Philly off course, but there’s also the knowledge that skilled 7-footers that can walk and chew gum at the same time tend to make teams better. And that no other team in the East’s bracket above Philadelphia looks to be in danger of falling out of the hunt right now.

The Celtics need an in-season turnaround, even if it only sees them start to average three wins for every five games played. Teams that lose four straight by almost 80 combined points don’t tend to average that rate of winning, though, even after adding a nice player such as Bradley or watching as a rookie like Jared Sullinger starts to understand defensive rotations. The “it’s a long season” fallback is usually outmoded by Christmas, the C’s have 51 games left and they need to probably win 29 of them to make it to the playoffs. It’s true that the Sixers are on a 38-win pace, right now, but that could change once Bynum returns.

Boston gets no such Bynum, and Garnett’s minutes won’t be amped up any time soon. It’s up to his teammates to find a way to play competent defense during KG’s well-earned trip to the pine.