Either injuries, defections, retirements, or just plain apathy doomed these teams from the beginning, in their quest to repeat as champions.
1) '98-'99 Chicago Bulls
No team in NBA history has had a more significant turnover from one year to the next than the Bulls in '97-'98 to '98-'99. Fresh off winning his sixth NBA title and fifth regular season MVP, Michael Jordan retired again, this time more definitively. Even though it was a heavy rumor throughout the 1998 postseason, his retirement announcement was not immediate. Right after the 1998 NBA Finals concluded, the league's owners began a prolonged lockout on the same day Phil Jackson stepped down as Bulls coach. Perhaps Jackson knew first-hand at that point that Jordan wasn't returning, or perhaps he was just wisely reading the writing on the wall. Either way, it was an obvious blow to general manager Jerry Krause's attempts to coax Jordan into staying, and his star publicly announced that he wouldn't decide on his playing status until the lockout was lifted. That wound up taking over six months to happen, and on January 13th of 1999, Jordan officially announced his retirement, leaving Chicago scrambling to rebuild the team on an accelerated timeline due to the lockout negating the traditional free agency period. Within 10 days of that announcement, Scottie Pippen (traded to the Rockets), Dennis Rodman (released), Luc Longley (traded to the Suns), Steve Kerr (traded to the Spurs), and Jud Buechler (released) had all followed Jordan out the door, while Iowa State coach Tim Floyd had been hired to replace Jackson. The only prominent Bulls players that returned for '98-'99 were Toni Kukoc, Dickey Simpkins, and an aging Ron Harper. Their biggest free agent move was signing Brent Berry, who had been unceremoniously cut by the Heat, and their first round pick, Oregon State's Corey Benjamin, lasted just three mediocre seasons in the NBA. In short, the team was a mess, though they did manage to avoid finishing with the league's worst record, as their 13-37 mark placed them ahead of the Clippers (9-41) and Grizzlies (8-42). It was an unprecedented campaign, as the Bulls became one of only three title winners to finish below .500 the next season, one of just two to miss the playoffs entirely, and the only defending champ to finish in last place in the conference. It would take six more seasons, four more head coaches, and six top 10 draft picks before the Bulls were respectable again in '04-'05.
2) '80-'81 Los Angeles Lakers
Unlike the Bulls two decades later, the '80-'81 Lakers had the same head coach and core group of players that won the title in the prior season. But the relationship between that coach and his star players deteriorated throughout the season, and it came to a head during the playoffs. Things started promisingly enough, with the Lakers holding a record of 15-5 out of the gate until Magic Johnson suffered the first major injury of his career, a knee cartilage tear which caused him to miss almost four full months of action. It was a blessing in disguise for Norm Nixon, who was allowed to shift back to his natural point guard position and run the offense again. When Johnson returned in late February and resumed his spot in the starting lineup, Nixon agreed to return to shooting guard, but not without leaking quotes to the media claiming that Johnson was receiving unfair deferential treatment from the coaches and owners. It didn't help that Nixon was also one of several Lakers whose name was being bandied about in trade rumors, as owner Jerry Buss was attempting to add Denver's David Thompson to the roster. No major trade ever materialized, and the Lakers entered the playoffs with the third seed in the West and their current roster intact. With Johnson still out of shape from his injury rehab, Nixon obviously disgruntled, and other players like Kareem Abdul-Jabbar seemingly distracted by the dysfunction, the Lakers were shocked in the first round of the playoffs by Moses Malone and the Rockets. Westhead survived into the '81-'82 season, but was fired after a slow start and replaced by Pat Riley, who led the team to a victory in the 1982 NBA Finals. Nixon stayed with the team through the '82-'83 season (he was even an All-Star in '81-'82) until his trade demands were finally met, and he was shipped to the Clippers for Byron Scott.
3) '48-'49 Baltimore Bullets
In its inaugural '46-'47 season, the NBA (then called the BAA) featured 11 teams, only three of which - the Celtics, Knicks, and Warriors - are still active today. In fact, after that season ended with the Warriors defeating the Chicago Stags in the 1947 BAA Finals, four (the Toronto Huskies, Pittsburgh Ironmen, Detroit Falcons, and Cleveland Rebels) of the 11 franchises folded before the '47-'48 season began. The BAA responded by bringing in the Baltimore Bullets, reigning champions of the American Basketball League (ABL). No one expected them to contend right away, as the ABL was a loose coalition of semi-pro teams across the Eastern seaboard while the BAA had most of the country's top-level basketball talent. But led by legendary player-coach Buddy Jeannette, the Bullets stunned the Knicks, Stags (who folded in 1950 and have no relation to the Chicago Bulls), and Warriors in succession in the playoffs to win the 1948 title. It was a long time coming for Jeannette, who had spent most of his formative years in the dilettantish barnstorming circuit, then toiling away almost anonymously in the ABL. The BAA expanded again in '48-'49 after a merger with the rival National Basketball League (NBL), bringing in star talent like George Mikan on the Lakers and Arnie Risen on the Royals. Even though the league was now tougher and Jeannette was starting to struggle at age 31, which was basically ancient for an athlete back then, the Bullets were still competitive thanks to a trade for rising star center Connie Simmons, and they snuck into the playoffs despite a losing record. But they were eliminated in the first round by the Knicks, and to add insult to injury, the cash-strapped Bullets management traded Simmons to that very New York team later that summer. Baltimore would reach the playoffs just one more time in '52-'53 before the franchise folded in 1954.
4) '83-'84 Philadelphia 76ers
The '82-'83 76ers season was a culmination of years of roster building by general manager Pat Williams, with a trade for Moses Malone as the final centerpiece. After they rampaged through the 1983 playoffs and cemented their place as one of the greatest teams of all time, a letdown in '83-'84 was inevitable. The issue didn't seem to be age, as only Julius Erving and Bobby Jones were on the wrong side of 30 at that point, and it really wasn't injuries, as all the core players missed a few games but no one was out for more than 11. Though his stats did dip a bit from previous MVP campaigns, Malone still averaged 22.7 points and a league-leading 13.4 rebounds per game. The main issue, much to long-time head coach Billy Cunningham's dismay, seemed to be overconfidence from the veteran roster that they could just flip the switch come playoff time. Finishing second in the Atlantic division behind their rivals in Boston, the Sixers drew a young, hungry Nets opponent in the postseason first round. New Jersey out-hustled the Sixers at every turn, and won all three games at the Spectrum in a stunning five-game series upset. The Sixers did bounce back in '84-'85, thanks to a talent infusion from rookie Charles Barkley, making it back to the Conference Finals one last time with Malone and Erving.
5) '11-'12 Dallas Mavericks
Their story is similar in many ways to the '98-'99 Bulls, in that a pending lockout chipped away at their championship momentum, and wreaked havoc on their roster retention. When the lockout was lifted in November of 2011, Dallas immediately lost their defensive anchor, center Tyson Chandler, who signed as a free agent with the Knicks. Key rotation pieces DeShawn Stevenson, Caron Butler, and J.J. Barea followed Chandler out the door, leaving Dallas scrambling to fill spots with shaky veterans like Lamar Odom, Vince Carter, and Delonte West. Sure, they kept their star Dirk Nowitzki and brilliant coach Rick Carlisle, but that would prove to be not nearly enough to mount a respectable title defense. When the season finally started on Christmas Day, the joyous occasion of finally receiving their championship rings was tempered by Dallas getting blown out of their own gym by the Miami team they had defeated in the 2011 Finals. It was a sign of things to come, especially as significant time was lost to injury for Carter, West, Jason Kidd, and Brendan Haywood, while Odom suffered through a season full of distractions and setbacks. Thanks to some typically astounding performances from Nowitzki, Dallas was able to make the playoffs as a #7 seed, and put up a fight against the Thunder in the first round before ultimately bowing out in a four-game sweep. It was the beginning of the end for the Mavericks, who have still not won a playoff series since that 2011 championship.
6) '06-'07 Miami Heat
Already a title contender with Dwyane Wade taking the league by storm, the Heat got a further boost early in the '05-'06 season when Stan Van Gundy stepped down as coach and was replaced by Pat Riley. They also benefited from playing in a weak conference and especially weak division, allowing them to coast down the stretch and rest their aging charges like Shaquille O'Neal, Antoine Walker, and Gary Payton while still cruising comfortably to the conference's #2 seed. '06-'07 was a completely different story. It started with Wade, who missed significant time due to injury, including a shoulder separation that had him considering season-ending surgery. O'Neal, Walker, and Payton were all decreasingly effective, as were fellow veteran holdovers Alonzo Mourning, Jason Williams, and James Posey. Despite bringing back essentially the exact same roster and coaching staff, the Heat were like a completely different team and it was apparent from the start, as they lost their season opener to the Bulls by 42 points. Miami was still good enough to win the Atlantic division, but as the #4 seed they drew those same Bulls in round one. It was a nightmare matchup, with Chicago pounding away at the Heat for four straight games. Fans and pundits kept assuming that Miami would turn it on and turn it around at every turn, but they were eventually swept, with an especially embarrassing 92-79 loss in the game four clincher. The team went into full rebuilding mode the next year, trading away O'Neal and Walker, letting Posey walk as a free agent, losing Payton and Williams to retirement, and setting up Erik Spoelstra as Riley's replacement.
7) '56-'57 Philadelphia Warriors
Long before the '06-'07 Heat or '11-'12 Mavericks were swept in the opening playoff round as a defending champion, the '56-'57 Warriors were the first to accomplish that feat. Led by foundational stars like Joe Fulks and George Senesky, the Warriors were a powerhouse in the early NBA, winning the inaugural title in 1947, reaching the Finals again in 1948, and making four more consecutive playoff appearances from there. But they were struggling in the mid '50s, despite the presence of the league's two leading scorers in Paul Arizin and Neil Johnston. They hired their former playing legend Senesky as their new head coach in 1955, and drafted a new young star in Tom Gola. The turnaround was remarkable, as Philly dispatched of their rival Syracuse Nationals in the Conference Finals, then the Pistons in the NBA Finals. Just as quickly as they improved in '55-'56, things fell apart the next year. Gola missed the entire season with a knee injury, and without the heart and soul of their defense the Warriors couldn't contain any opponents, least of all the newly dynamic Celtics, led by Bill Russell and Bob Cousy. They finished third in the division behind Boston and Syracuse, then fell to the Nationals in the first round in a two-game sweep, as center Red Kerr took full advantage of the Gola-sized hole in the middle. The Warriors came back improved in '57-'58, but by then the Celtics were fully dominating the conference, and it wasn't until landing Wilt Chamberlain in 1959 that they were a serious contender again.
8) '69-'70 Boston Celtics
When Bill Russell retired after the 1969 NBA Finals, the Celtics lost not only the greatest player of all time up to that point, but also a successful head coach. After Red Auerbach stepped down as coach in 1966 and transitioned full time to the front office, Russell picked up the clipboard as player-coach for the last two Celtics titles of his dynasty. Subsequently replacing Russell on the sidelines in 1969 was Tommy Heinsohn, his longtime teammate. Though Heinsohn would eventually find success as Boston's head coach, leading them to titles in 1974 and 1976, his first season at the helm was anything but smooth. Replacing Russell at center was Hank Finkel, a former All-American at Dayton whom Auerbach traded for from the Rockets. He was serviceable in '69-'70, contributing 9.7 points and 7.7 rebounds per game, but hardly at the level of Russell, who not only provided stats but was a premier play maker and the heart-and-soul of the defense. In addition to Russell's departure, the Celtics also lost the legendary Sam Jones to retirement, while core veterans Satch Sanders, Bailey Howell, and Larry Siegfried were all aging fast and struggling to take on increased roles. With longtime rivals like the Knicks, Royals, 76ers, and Lakers seeming to revel in getting some revenge on them, the Celtics received no quarter from their opponents, and finished the '69-'70 season at 34-48. It was the first time in 20 years that the team had finished below .500 or missed the playoffs. But to the dismay of their opponents, the struggles didn't last long in Boston. Finkel gave way to rookie sensation Dave Cowens in '70-'71, and the Celtics reached at least the Conference Finals for five straight years starting in '71-'72.