Since the start of Michael Jordan’s first title run, only two teams have won the championship while ranking outside the top 10 in points allowed per possession: the 2000-01 Lakers and the 1994-95 Rockets. Those Lakers famously relaxed for much of the regular season before flipping the switch during a devastating playoff run, while the repeat Rockets changed the entire complexion of their team at the trade deadline in the Clyde Drexler–Otis Thorpe deal. They are each anomalies in their own way.

In that same 20-plus-year span, only 15 teams have even advanced to the conference finals while ranking outside the top 10 in points allowed per possession — less than one per season. All but two of those teams ranked among the league’s top three offenses, and seven topped the league in points scored per possession; the Steve Nash Suns alone take up three of these slots.

In other words: Teams that are even just average defensively have very little chance of doing much damage in the postseason unless they score at a lights-out rate. The reverse also applies, though not quite as strongly; most studies have found that an elite defense is slightly more important to building a champion than an elite offense.

The Brooklyn Nets front office, in honest moments, would admit that this team is not a title contender right now, primarily because it will have issues building an above-average defense — and also because Miami is entering its prime as a team. The major challenge for the Nets this year and going forward will be slowly building toward a top-10 defense with a Brook Lopez–Kris Humphries front line, or failing that, finding the new players necessary to pull off the trick despite a severe lack of cap flexibility that could prevent the Nets from using even the full mid-level exception until the summer of 2016.

It’s no secret the Nets are going to have issues on defense. Lopez has been something of a punch line for two years now, owing mostly to his miserable rebounding numbers. The Nets have been among the league’s 10 worst defenses each season since he entered the league, and they have consistently played much worse on that end when Lopez is on the floor, per NBA.com and Basketball Value. Humphries, Lopez’s front-line partner, is a worker and a glass-eater, but effort alone can’t make up for deficits that are more or less unchangeable. Humphries isn’t especially tall or fast, he doesn’t have long arms, he’s not a great leaper, and though he generally has good intentions, he doesn’t have the genius-level innate understanding of space, timing, and angles that can turn a so-so defender into a very good one. And it’s very hard to find teams that have won titles without at least one very good big-man defender.

The Nets understand this, and they have taken some basic steps to remedy the damage. They are huge on the wing, with Joe Johnson and Gerald Wallace both (in theory) capable of working as top-shelf gang rebounders on the defensive glass. Wallace can play power forward in the right matchups, giving Avery Johnson some insurance against both the Humphries-Lopez front line and the total uncertainty surrounding all of Brooklyn’s backup bigs. (Seriously: The Nets look deep, but how many players on this roster are actual, proven, good NBA players? Perhaps only six: Deron Williams, Johnson, Wallace, Lopez, Humphries, and C.J. Watson, a solid backup point guard. MarShon Brooks will probably join the list, but after that, it’s one-dimensional guys such as Reggie Evans, amnesty cuts in Josh Childress and Andray Blatche, a washed-up veteran in Jerry Stackhouse, and at least one intriguing rookie who may or may not be able to defend his position in Mirza Teletovic.)

Wallace ranked 13th among all small forwards in defensive rebounding rate last season, tied with Michael Beasley and Linas Kleiza, which means he projects as solid but hardly a Bobcats-era game changer on the glass as he enters his 30s. Johnson’s size suggests he’s an elite rebounding guard, but the numbers don’t; he had virtually the same defensive rebounding rate as Ray Allen and Ty Lawson last season — about average among all guards, and the norm for Johnson’s career. He can jack things up in a new context, but he’s not going to morph into Evan Turner.

Still, the Nets were an average defensive rebounding team in 2010-11, and they’ll hold their own whenever Humphries is on the floor. What happens when he hits the bench is unclear; their defensive rebounding rate in 2010-11 plummeted from 76.8 percent to a league-worst-level 70.9 percent when Lopez played without Humphries.

The larger issue will be rim protection, especially when teams go at Lopez either directly or indirectly in the pick-and-roll. The Nets’ defense over the past four seasons has allowed a ton of shots in the restricted area; only nine teams allowed more in 2010-11, when Lopez last played a significant number of games, and New Jersey allowed that many close attempts despite playing at one of the league’s slowest paces and fouling a ton — wiping away official shot attempts in the process. The trend has actually been worse in other seasons; only one team allowed more shots at the rim in 2009-10, and only two did so last season, when Lopez barely played, per Hoopdata.

The Nets during that same stretch have allowed a below-average number of 3-point attempts — generally a good indicator. But shots at the rim are the highest-value attempts in the game, and it’s worth asking if Avery Johnson and his staff should work more aggressively to limit them, even if it means allowing more 3-pointers from non-corner areas.

There are lots of ways for big men guarding screeners to defend the pick-and-roll, but Lopez almost always does this:

In clip after clip, it’s the same: As the Nets’ point guard chases his opponent over the screen, Lopez simply sags back toward the foul line area or even lower. That’s a common strategy for slow-footed bigs. The goal is to keep that ball handler above the foul line until the Nets’ guard can recover and find his man again, allowing Lopez to shoot back to the big man rolling toward the rim. It’s not an ideal strategy, since Lopez is surrendering wide-open mid-range shots. He’ll occasionally step out a bit farther against Nash/Chris Paul–level shooters, but he’s never been consistent about it, and those guys eat him up either way — by sinking mid-range jumpers when open, or blowing by Lopez when he steps above his comfort zone.

But mid-range shots are the lowest-value attempts in the game. Good NBA offenses force defenses into choices, and giving up mid-range jumpers isn’t a bad choice. Problem: The strategy hasn’t actually forced offenses into that outcome. They’re getting to the rim anyway, especially when Lopez is on the floor. In 2010-11, a whopping 35 percent of opposing field goal attempts against the Nets came at the rim when Lopez played, and opponents hit 60.5 percent of them, according to NBA.com’s stats database. When Lopez sat, those numbers fell to 31 percent of attempts and 54.9 percent accuracy. The split was nearly as dramatic the year before.

The tape reveals several reasons for this. Lopez just isn’t an effective defender, in terms of speed, technique, or jumping ability. Lopez actually isn’t a spectacularly bad defender, in a JaVale McGee/Blatche/Amar’e Stoudemire way that makes you question his competence and/or effort. He mostly tries, and in the way he shifts around the floor, he shows an ability to monitor both ball and man at once. He doesn’t recklessly chase shot blocks, and he’s actually sort of good at using his length to bother perimeter players who get a step on him.

Lopez’s issues are more boring. That’s the thing about the Nets. They’re a sexy team because of Brooklyn and Jay-Z and those black uniforms, but their problems are totally unsexy. They will determine their own ceiling based on how well they do all kinds of little things that happen dozens (hundreds?) of times in every NBA game.

Back to Lopez’s sagging, and why it often fails. Speedy guards just aren’t scared of Lopez crouched there at the foul line. They are confident they can get around him, and really smart ones, like Tony Parker, just drive straight at his chest, knowing Lopez has a tendency to stand straight up and backpedal, making it hard for him to re-settle himself for a legitimate shot-block attempt. That technique can also get him stuck under the rim, off-balance.

Those guards also know that if they manage to get inside the foul line, Lopez must make a more serious commitment to them by following them to the hoop or making an extra step toward the sideline. That in turn takes Lopez farther from his own man, rolling open to the rim, and that is where Humphries’s own ho-hum limitations come in. It’s often his job to rotate to Lopez’s guy in this situation, and he’s just not especially fast or adept at changing directions.

Again, there’s nothing fancy about any of this, or about solving it. The other four Nets defenders may just have to be primed earlier to crash into the paint, prepping for crisis even as an opposing team sets up for a pick-and-roll. That’s on everyone — on Humphries, or whoever is in primary help position, and on the wing players responsible for crashing down on Humphries’s man. That could mean being one step closer to the paint than has been typical for the Nets’ perimeter guys, both in Jersey and their previous destinations. Tom Thibodeau’s defenses in Boston and Chicago, and their imitators league-wide, have been playing this kind of aggressive style for years — overloading the strong side early with an extra defender to keep the ball out of the paint at all costs.

The cost, of course, comes in leaving those weak-side shooters open for swing passes. The very best defenses can limit the damage through sheer talent, learned instinct, and preparedness. With their size and skill, Wallace and Johnson would appear to have the goods to execute this kind of crash-and-recover-outside stuff pretty well, though they are aging and don’t bring the same killer athleticism as Dwyane Wade and LeBron James.

Avery Johnson, throughout his career, has been a vanilla defensive coach in terms of X’s and O’s, though one who clearly inspired his Dallas teams to make huge strides on that end. Will he load up more heavily on the paint this season? And if he does, will the Nets make the optimal rotations behind the inside action? Guys have to make split-second decisions on where and how to rotate depending on the location of specific opposing shooters. Non-corner 3s are less dangerous than those from the short corner, and abandoning guys in the corner closest to the guard on the pick-and-roll is generally a no-no — especially when smart teams station an elite shooter in that corner, knowing the pressure it places on defenses.

There will be other issues beyond high pick-and-rolls targeting Lopez. The side pick-and-roll against Humphries will be a regular anti-Nets weapon. Unlike Lopez, Humphries has a tendency to blitz ball handlers on the pick-and-roll, like this:

Screeners who cut immediately to the rim are thus able to roam free, in turn putting pressure on Lopez to be ready to help in the paint. Teams will start this action with Lopez’s man on the other side of the floor, knowing Lopez won’t be able to get into the paint early because of the defensive three-seconds rule. Historically, Lopez just hasn’t been early or strong enough with his help to prevent big guys with good ballhandling skills from going right up and through him at the basket. He’ll have to be better and earlier, and that will require his having confidence in the wings behind him to be just as good and just as early. If Lopez can’t manage it, more dramatic outside-in help might be necessary.

Another area to watch: transition. The Nets have ranked 26th, 24th, and 23rd in points allowed per possession in transition in the past three seasons, according to Synergy Sports. Lopez is slow. Humphries crashes the offensive glass and has a bad habit of watching his own jumpers as his guy leaks out. Both take an extra beat to gather themselves for quick directional changes, making them vulnerable to early pick-and-roll action in delayed transition, before they have a chance to set their feet.

And we haven’t even gotten to Teletovic and Blatche. The former is totally unproven as an NBA defender and has predictably looked confused in preseason. Blatche looks to be in great shape, and the Nets are thrilled with him so far, but he’s still Blatche until further notice. His issues on defense always went beyond effort and into the murkier territory of positioning, timing, and smarts.

The Nets understand all of these challenges and how teams will go after them. They should develop into a very good offensive team, with enough post-up threats, passers, and shooters among their rotation guys to attack in a variety of ways. They can go small, with Wallace at power forward. But if they can’t build an above-average defense, they’ll never win a championship with this core. That project has just begun, and it will require constant vigilance and tweaking from everyone involved. The uniforms, arena, 40/40 Club, and Calvin Klein VIP entrances are all very nice, but the Brooklyn Nets are a basketball team now, with the same challenges every other basketball team faces.