BOSTON — His team’s defense in a maddening two-month erosion, Boston Celtics coach Brad Stevens made the (maybe slightly overdue) decision to alter his starting lineup Tuesday night with Aron Baynes paired up front with Al Horford during a gritty Kyrie Irving-less win over the Cleveland Cavaliers.

The two-big lineup made things tough for Cleveland’s sizable frontline and helped Boston produce one of its better recent defensive efforts. Horford took every opportunity to gush about Baynes’ impact in the aftermath.

"I just think that anything with Baynes works,” Horford said after Boston’s offday workout on Wednesday. “[Baynes] does so much for us, defensively. Protects the rim, just a very smart defender, and … whether it’s me, [Marcus] Morris, Guerschon [Yabusele], whatever, and I just feel like he makes our defense better.”

It’s hard to argue with the numbers. 

The Celtics now own a defensive rating of 83.9 in the 95 minutes of floor time that Horford and Baynes have been paired this season. That’s not just a stellar number on its own for a team that ranks fifth in the NBA allowing 107 points per 100 possessions, it’s also the best defensive rating among the 79 two-man units that have played at least 50 minutes for Boston this season.


And it isn’t an anomaly. The Celtics paired Horford and Baynes together in the team’s most common starting lineup last year and got elite-level defensive play. Boston owned a defensive rating of 93.9 in the 863 minutes the duo was paired, and the Horford/Baynes combo had a sizzling net rating of plus-11.8 overall.

So why in the world are the Celtics not rushing to reunite this pairing and make it the starting frontcourt moving forward? 

There’s a few issues at play, not the least of which is that moving Baynes into a starting role leaves Boston’s reserve groups dangerously thin on bigs with both size and experience. The bigger concern: the NBA’s small-ball trend that makes it hard to see how the Celtics can survive leaning hard on two-big lineups.

“Obviously, the challenge of the league is guarding a lot of the spread teams,” said Stevens. "Night in and night out, it is a different challenge, so there are some lineups and some teams that you might play that against more, and some lineups that are really hard to play that against. But, generally, I think [Horford and Baynes] bring a real defensive DNA, and I think they're very committed to doing whatever it takes to make it really hard to score on them. 

"With their size and length, I think we have a different impact at the rim. But when you're playing a team that's super small and spread out, that's tough to guard when you have a more traditional lineup.”



To hammer home that point, just look at the numbers from Boston's 19-game playoff run last year. The Celtics' defensive rating with the Horford/Baynes combo spiked to 103.7 — still a decent number, though defensive ratings tend to dip in the playoffs — but Boston was a minus-1.7 overall as their Kyrie-less offense struggled to generate consistent points. The Horford/Baynes combo struggled and the Celtics more often needed offense on the court. 

Even after Tuesday’s strong showing, Celtics players didn’t hide from the fact that two-big lineups can only be utilized now in certain situations.

"There’s going to be times [to utilize two bigs]. I don’t think we can play with those two on the floor at the same time just for matchup reasons because not every team plays a traditional two-big lineup,” said Secretary of Defense Marcus Smart. "But when we do, nine times in 10, it’s in our favor and it allows Al to step out on the perimeter and feel more comfortable and not have to bang and put that much pressure on his body on the defensive end. Baynes takes up that load and they complement each other.”

Here’s maybe the bigger concern with starting Baynes: Suddenly reserve groups have to lean hard on the likes of Daniel Theis (or Guerschon Yabusele or Robert Williams) for big minutes. Theis can hold his own against floor-stretching bigs but struggles against size. He logged only nine minutes in that Cleveland game and had a defensive rating of 152.4 in that span.



So what is Stevens to do?

His best bet will be to explore some of his more versatile lineups moving forward and hunt opportunities, based on matchups, to get some stretches with Horford and Baynes together.

The Celtics can leave Marcus Smart in the starting lineup and shuffle, say, Gordon Hayward back to the starting group. Or Stevens can dial it back to opening night and trot out the Newport 5/Erotic City combination of Irving-Hayward-Jaylen Brown-Jayson Tatum-Horford. Either of those groupings allows Morris and Baynes to provide size off the bench without having to lean heavy on the less experienced bigs.

Recent playoff runs have proven that it’s best to have some fluidity in the lineup. Matchups will dictate how personnel is dispersed with Stevens able to make adjustments on the fly should they encounter unexpected struggles.

Versatility and depth were always supposed to be the hallmarks of this Celtics team. While it’s understandable that players prefer to know their roles during the regular season, the best teams are the ones that can lean on 10 players and best line up their personnel based on what can exploit an opponent’s weaknesses.

Stevens opened his test kitchen over the final eight games, starting with the Baynes/Horford experiment. He can shuffle his cards again knowing that, presented with two-big opportunities, they’ve got a potential trump card. Now, the key is figuring out how to best deploy the myriad of small-ball lineups that Stevens can call for this postseason.

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