Do the Celtics have the pieces to be a good defense?

The Boston Celtics will feel the loss of Al Horford at both ends this season, but particularly on the defensive end of the floor.

I’ve been trying to figure out what to make of the Boston Celtics for weeks now.

Losing Kyrie Irving and Al Horford in free agency seems like it should matter a lot. Those guys are really good players, and they anchored the team on each end of the floor. But removing Irving’s apparently corrosive effect from the locker room and replacing him with Kemba Walker also seems like it should help things more than just a bit.

Already, the younger players on the team (Jayson Tatum and Jaylen Brown, in particular) seem more invested in the culture and chemistry of this year’s team that has yet to take the floor than they were in last year’s group that was smoked by the Bucks in the second round of the playoffs. All you have to do is listen to literally anything coming out of Team USA camp to realize that.

Walker is a reasonable enough facsimile for Irving that the team should not lose much in the way of production at point guard, and though he is older, Kemba is less of an injury risk than Kyrie, given their respective histories. He does not have quite the same variety of moves and fakes and angles and trick shots as Irving, but he comes pretty close, and he’s damn near as effective without all that stuff anyway. Throw in whatever benefit the team gets from his leadership/aura/personality combination and how his disposition allows for Tatum, Brown, and some of the other younger players on the team to flourish, and you can see the offense remaining average or better — even without the combination of shooting and playmaking Horford brought to the table.

But the thing I keep coming back around to is the defense. Irving and Walker are likely a wash on that front, though Walker gives more consistent effort and is less prone to boneheaded mistakes. His size renders him less effective than his effort and attention would merit, and it’s extremely difficult to be an impactful defender at the point guard spot anyway. But the real loss here is Horford, and, to a lesser extent, Aron Baynes.

The Brad Stevens-era Celtics have a strange track record on the defensive end of the floor. They have developed a reputation as a consistent lockdown type of group, but that has not exactly been the case. Stevens’ Celtics have finished in the top six in defensive efficiency three times but checked in 12th, 14th, and 17th in his other three seasons.

All of that has combined to give his Celtic teams an average ranking of the ninth-best defense in basketball; but it’s notable that when taking a look at their performance in the Four Factors, the only area where his teams have even semi-consistently shown elite results is the one over which defenses have been shown to have the least amount of control: shot defense. They have been below-average at both avoiding fouls and preventing offensive rebounds, and only slightly better than average at forcing turnovers.

Swapping out Horford and Baynes and awarding most of the center minutes to Enes Kanter, Robert Williams, and Daniel Theis all but guarantees a drop-off in Boston’s shot defense. Horford is one of the very best big man defenders in basketball; his ability to work both in space and near the rim is not something the team could have replaced with any one player in the first place, but it certainly cannot do so with the cast on hand.

Perhaps more responsibility can be soaked up by Tatum, Brown, Marcus Smart, and Gordon Hayward. Perhaps Williams is ready to be an interior force. Perhaps Kanter can have the best defensive season of his career. Perhaps Semi Ojeleye can turn into a consistent presence or Grant Williams can be the rare rookie to have a positive impact defensively. But even if all that happens, it’s not likely to completely mitigate Horford’s absence. And that’s before we get to Baynes, who just accentuated Horford’s strengths when they shared the floor and was at least able to approximate his interior impact when he played as the lone big man.

If Boston’s shot defense drops back toward the middle of the pack, how will Stevens’ team make up for it? They have not shown a consistent ability to do any of the things that would help offset such a drop. With Smart and Brown as likely the two best defenders remaining on the roster, this would have to be a defense constructed around its perimeter talent. Such defenses most often reach elite status either through versatility or the forcing of turnovers.

Stevens’ teams have only occasionally been high-level pilferers, and the likelihood of his suddenly becoming a coach whose teams switch everything (or close to it) seems low — especially with Walker and Kanter likely to play big roles in that defense, given how ill-fitting they are for such a system. Kanter should help in the rebounding department, but playing him big minutes has almost always meant death for a team’s defense throughout his career. He held his own a bit better for a while last season in Portland, but when it came time to play the Warriors, he was lost once again. Maybe the answer lies in ramping up the pressure, but that could lead to foul issues, an area where even the recent excellent Celtics defenses have had some trouble.

None of this is to say that the Celtics can’t find their way into being a top-10 defense with this roster. Certainly, stranger things have happened. It just figures to be much more difficult to accomplish with this group than Stevens has found it in the past. And unless they can post significantly better offensive results than most Celtics teams of recent ilk, that means they’re likely to fall short of expectations.