How the Celtics pulled off one of the greatest rebuilds ever to become the team that should terrify the NBA

• A combination of savvy trades, draft picks, and player development have positioned the Boston Celtics to become the NBA's next contender.
• The Celtics wowed the NBA world with a deep playoff run, despite missing Gordon Hayward and Kyrie Irving, showing off how talented their young core is.
• Members of the organization credit GM Danny Ainge and head coach Brad Stevens for creating a hard-working, meticulous culture.
• The Celtics are positioned to keep improving, but their current team may be good enough to contend for a championship when they welcome back Irving and Hayward.

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For about five minutes, Boston Celtics president Rich Gotham liked his team's chances.

"I honestly sat there and said to myself, 'Wow, I don't think Cleveland's gonna be able to guard us this year,'" Gotham told Business Insider.

Then, less than six minutes into the 2017-18 regular season, tragedy struck the Celtics. Newly signed All-Star forward Gordon Hayward landed awkwardly on an alley-oop attempt and suffered a gruesome ankle injury that ended his season.

The Celtics, a star-studded team, primed to challenge for the Eastern Conference, were suddenly without one of its key cogs.

The team marched on anyway, winning 16 of its first 18 games and taking the league by surprise. They finished second in the East with 55 wins.

Then, another setback: Kyrie Irving would miss the entire playoffs after undergoing knee surgery. A team already short on scoring would have to go to the postseason without its best scorer.

Nobody would have blamed the Celtics for folding after the Irving injury. Instead, they rallied, getting even bigger production out of players like Al Horford, Jayson Tatum, Jaylen Brown, Terry Rozier, and Marcus Smart. The ragtag Celtics took down the Milwaukee Bucks in seven games, the upstart Philadelphia 76ers in five, and nearly took down the Cleveland Cavaliers in the Eastern Conference Finals, all with $48 million in salary sitting on the bench.

"I think our expectations changed during the season," Gotham said. "We didn't feel like it was house money or a bonus year; we felt like we were playing to win. What was great, the bigger the challenge got, the more our players stepped up."

"I think everybody would probably say [they were surprised]," Todd Lickliter, a former Celtics scout, said. "They achieved at the highest level you could have expected them to, and they responded so well."

The Celtics playoff run was a testament to what they've built over the years. The 2017-18 roster only had four returning players from the year before, but the groundwork was laid years ago. Through savvy transactions, player development, and a coach quickly joining the NBA's elite, the Celtics look like the NBA's next contender.

"No one walked out of that gym after Game 7 [of the Eastern Conference Finals] feeling anything but bitterly disappointed that we lost an opportunity to go to the Finals," Gotham said. He added: "We didn't feel like, 'Oh well, we shouldn't have made it this far.' ... I think next year, the expectations stay the same."

There's the scary thought for the rest of the league - this Celtics team, a year older, welcoming back its two star players. It's the latest step in what is quickly turning into one of the greatest rebuilds the NBA has ever seen.

The trade that started it all.

The Celtics wouldn't be where they are without first having decided to blow it up five years ago.

The 2013 Nets-Celtics blockbuster deal lives in infamy. The unprotected picks the Nets sent the Celtics for Kevin Garnett, Paul Pierce, and Jason Terry ended up becoming lottery picks that fell into the rebuilding Celtics' lap.

The 2016 pick turned into Jaylen Brown, an explosive, do-it-all wing who took significant strides in his second season. The Celtics traded the 2017 Nets pick, which was first overall, to the Philadelphia 76ers and acquired a 2019 lottery pick as a bonus. They used the third overall pick they got from the 76ers on Jayson Tatum. The 2018 pick was used to acquire Kyrie Irving in a blockbuster trade with the Cavs.

Just as important were the moves the Celtics didn't make. ESPN reported in 2015 that the Charlotte Hornets turned down an offer from the Celtics that included as many as five picks to move up in the draft to get Justise Winslow.

"There was a time when I thought, 'Woah, this is getting a little out of control' ... In the long run, maybe it'll be the best," GM Danny Ainge told ESPN at the time.

They chose to stand pat at the 2017 trade deadline when players like Paul George and Jimmy Butler were reportedly available, balking at the prices the Indiana Pacers and Chicago Bulls set, respectively, for the star wings.

"It can be hard to stay patient, but I think, sometimes they say the best deals you make are the ones you don't make," Gotham said.

It's hard not to look at the Celtics and think that when Ainge does play his hand, he tends to win.

The pieces the Cavs acquired for Irving have not had much impact. Isaiah Thomas and Jae Crowder were traded away midseason. Ante Zizic played just 23 minutes in the postseason. The 2018 Nets pick is eighth in the draft, a solid but unspectacular position.

The trade down in last year's draft also seems to have far-reaching implications. With their eyes on Markelle Fultz, the 76ers swapped picks with the Celtics and sent Boston a 2019 lottery pick that could end up as high as No. 2 in next year's draft (depending on some complicated pick-swapping and protections).

Fultz played just 14 games in his rookie season because of a bizarre shoulder injury. Tatum looks like the crown jewel of the Celtics' rebuild, something that may not have happened without a workout that blew away the team.

The workout that may transform the franchise.

The Celtics were informed that Jayson Tatum was under the weather before he went through a second pre-draft workout for them in 2017. The Duke forward had already done one workout in Los Angeles in front of some of Boston's basketball staff.

According to Gotham, Tatum put on a "clinic" in his second workout.

"Some of the best shooting I've ever seen," Gotham said.

The Celtics scouts had long liked Tatum, a star in his high school class, but weren't sure of him during his lone season at Duke. The team had some doubts about his three-point shooting before the workout. He convinced them otherwise.

It's hard not to view Tatum as the focal point of the Celtics' rebuild. The 19-year-old wowed in his rookie season with the utter ease with which he scored the ball. Some Celtics staffers have compared him to a young Paul Pierce.

The Celtics have several intriguing young players. Terry Rozier had a breakout playoff campaign and looked the part of a starting point guard; Brown may have All-Star potential. Tatum's ceiling is different - he may have MVP potential. It's not hard to imagine him slowly adding different skills to become a complete package.

Tatum showed it all in the postseason. In a 50-second span in the biggest game of his young career, Tatum crammed a dunk on LeBron James' head and then hit a step-back three.

ESPN's Zach Lowe wrote that the Celtics value Tatum so highly that they may not trade him straight up for Kawhi Leonard. There are mitigating factors - injuries, contract situations - but it's nonetheless a hint at how highly the Celtics view him.

The legend of Brad Stevens and the culture he's helped create.

Todd Lickliter was the head coach of Butler University while Stevens was an assistant. Lickliter said he used to run practices where his assistants could coach different squads in scrimmages. Lickliter called it a joy to watch Stevens work with players and coach through scenarios, showing off his natural chops for the job. Stevens later became head coach of Butler until the Celtics lured him away for a reported $22 million over six years.

If acquiring star players is the biggest challenge in the NBA, getting a coach that can truly elevate a team might be next. It's clear the Celtics have that in Stevens.

Those around the Celtics credit Stevens for his preparation and attention to detail. Nothing goes overlooked.

"He goes over all the small details, which add up to big details at the end of the day," former Celtics assistant coach Walter McCarty, now the head coach at Evansville University, said. Stevens devours film, studying player tendencies and opponents' habits. "He pours over every single detail," McCarty said.

Stevens has become legendary for his after-timeout play calls. A few of them helped the Celtics win games in the postseason. McCarty has seen Stevens' basketball genius up close. McCarty told Business Insider that when Stevens draws up plays in timeouts, he can tell if the play will work as soon as the opponent's defense lines up.

"We got 'em," Stevens will say, triumphantly, forecasting how the play will go.

Stevens' work ethic and attention to detail permeate through the organization. Gotham, McCarty, and Lickliter all said if there's a common trait in the current Celtics' core outside of their obvious talent, it's their work ethic and desire to get better. Everyone is focused and driven in the organization.

Ainge's presence is critical to the culture, too. Ainge is known as one of the savviest and most ruthless GMs, willing to make any deal to improve the team. But those who know Ainge describe him as kind and humorous with genuine care for his players. McCarty, who also played under Ainge with the Celtics, said Ainge is known for making well-timed jokes to break up heated or intense practices.

"A lot of people, the boss comes around, they may tense up, or they might feel uneasy. Not around Danny. When he comes around, he's one of the guys."

Said McCarty: "He's one of those guys that whether you play here a year, four years, whatever, that door is always open with that relationship where you can call him up."

The mission isn't complete yet.

Add it all together, and the Celtics don't appear to have a weakness on the roster.

They'll have the length and athleticism to switch across several positions next year, making an already-stingy defense even stronger. They'll have multiple players capable of spreading the floor, making plays for others, or creating their own shot. Tatum and Brown are poised to get better. Again, they'll be welcoming back two All-Stars next season.

There's an obvious danger in getting complacent, and the Celtics won't merely rely on the team making a leap. 

"I've never been here in a season, regardless of how successful our team was in the prior season, where we didn't say, here are the improvements we need to make, here are the things we need to change to get better," Gotham said. "It's not always personnel; sometimes it is personnel. I'd say this year it's probably less about that."

There are decisions to be made and some unknowns. Marcus Smart is a restricted free agent this summer. One agent noted that Rozier's trade value might never be higher, and the Celtics might run into an issue with having too much depth.

There are already questions about Irving's future, as he hits free agency in 2019. He has said it doesn't make sense for him to sign an extension. Horford, the glue of the team, can become a free agent in 2019.

Hayward might not be the same player post-injury.

Ainge will always be on the hunt for upgrades, and he's positioned the team to make a go at another star.

The Celtics could have as many as four first-round picks next year, depending on how the draft order shakes out. The same agent noted that other players are intrigued with what the Celtics have built.

But the Celtics are also in the enviable position of opting not to make any drastic moves and seeing what they have with a fully healthy squad.

The Celtics have made back-to-back Eastern Conference Finals, and it appears their journey is just beginning. They aren't satisfied with the progress just yet.

"When we hang that next banner, maybe we'll sit back and say, 'You know, that was pretty good,'" Gotham said. "But not until then."