Sports message boards are rife with this kind of strife, even setting aside the classic, easily mockable (Yankees Suck!/Red Sox suck!) back-and-forths between fanbases. Within a fandom there is almost always a Broken Base. Best-case scenario, fans of a team will simply disagree on the quality of a given transaction. Over a long enough time, however, fans who frequently criticize management are usually accused of disloyalty or outright troll status, while those who frequently defend management are considered irrational fanboys incapable of independent thought. And that's without mentioning the cults of personality that tend to develop around certain players; if the two players should happen to compete for playing time with each other, the Flame Wars can get quite messy. Serious Business, indeed.
Go ask NHL fans how teams in warm weather cities are doing, and prepare to duck from the flames. On one side are fans who point to Dallas, San Jose and Anaheim as proof that the sport can succeed in places without snow; on the other are the fans who point to Florida, Atlanta and Phoenix as proof that the sport doesn't work in such areas, with Carolina, Nashville and Tampa used by both sides to prove their point. Don't even try touching the debate about whether the league should be on ESPN or NBC Sports Network in the US, either...
North American open-wheel racing:
The split (from 1996 to 2008): did you like Champ Car (more road racing and undoubtedly the more popular drivers up until around 2002) or the Indy Car Series (strictly ovals until 2005, including the Indy 500, but started adding non-ovals prior to the open-wheel reunion)?
After the split: The all-or-mostly ovals schedule that was part of the Indy Car Series' original plan, or the roughly 50/50 schedule between ovals and road/street courses that's taken effect since 2009? Do you like how similar the cars are, or does it turn you off? Is Danica Patrick a legitimately good racer or is she just eye candy that happened to get a win in 2008?
The Yankees/Red Sox rivalry: greatest rivalry in sports or the Creator's Pet of baseball due to its massive coverage by ESPN?
Women's American football
Lingerie Football League (LFL) vs. "traditional" women's football (WFA, IWFL, WSFL). The LFL proponents point to their organization's success, TV deal (with MTV 2), notable arenas, and major publicity, dismissing the fully-equipped women's leagues as groups of elitists who are beneath notice, noting that they don't have one-tenth the publicity that the LFL has. On the other hand, the traditional women's proponents' argument is more one of integrity, claiming they play "real" football closer to the NFL, NCAA, and high school rules, and the LFL is a cheap gimmick, with the women degrading themselves for the publicity.
Especially true in markets which are home to both LFL and WFA/IWFL/WSFL teams. It is not uncommon for the traditional women's team to challenge the LFL team to a scrimmage (in Chicago, the WFA's Force to the LFL's Bliss, in Cleveland, the WFA's Fusion to the LFL's Crush, and in St. Louis, the WFA's Slam to the LFL's Saints). Of course, no LFL team has accepted, or even answered said traditional team's challenge as of yet.
Rules of the game
College football's BCS. Is it really better than what there was before? What teams should be involved in a given year? Do teams from outside the power conferences have a fair chance? And the big one: Should the whole thing just be blown up and replaced with a playoff?
Now that the BCS will be replaced by a four-team playoff starting in 2014, the argument has shifted to how many teams should be eligible and how can a team be eligible.
A discussion of NHL fan opinion split that doesn't include the phrase 'shootout'? For shame. It's not just the fans that are divided, opinion of its effect on the game are divided amongst the players!
Also... fighting in hockey. Many hockey fans love a good tumble but there are many fans who refuse to watch the NHL but love the international juniors because of its clean fight-free play.
Dispute over different rules codes, or between supporters and opponents of a change in the rules. For example, the "designated hitter" rule in effect in Major League Baseball's American League (but not the National League) has its supporters and detractors. There are also differences in rules between professional and college football, and between professional and college basketball, the relative merits of which are disputed by fans of the sport.
Individual Players/Staff Members
LeBron James leaving Cleveland and going to Miami. Was it a betrayal of his homeland and team, or was it warranted, due to his team being ineffective and his free agency period allowing him to join another team? Was The Decision really that bad, or was it just a clumsy way to say where he was going to? Can we blame him for The Decision, or does it fall on the shoulders of ESPN for even giving it that much publicity? Was he flat-out cheating his way into a championship by teaming up with two superstars, or was it warranted, due to being the only competent man in his original team for seven straight years? Many agree that he got cockier afterwards, but does he still deserve the same amount of disdain since then?
Billy Beane and his "Moneyball" system either does what nobody else thought to do to - make a great baseball team on a shoestring budget, or created an overrated endlessly-copied system which makes for boring play and limited success in the postseason and gives cheap general managers an excuse for not paying people what they're worth. (For the uninitiated, he uses spreadsheets and such to determine from past statistics who the most underrated players are, and he rejects some flashy strategies like stealing in favor of whatever has the highest statistical probability of getting a run.)
Peyton Manning is either the Jesus Christ of professional American football, or he's an overrated, whiny douchebag who chokes in pressure situations. The latter group had mostly grown silent since the Colts won Super Bowl XLI, but their loss to the Saints was like miracle CPR to them, as Manning threw a critical interception in the fourth quarter of Super Bowl XLIV which ensured a Colts defeat.
Michael Vick, before, during and after his conviction and jail term for dog-fighting: "He's paid his debt. Leave him be" crowd vs. the "That dogkiller should be a pariah" crowd. There's also the third crowd: fans of the Eagles who say "Why did we hire this guy again? He can't win a game to save his life!"
Similarly (to an extent), Ben Roethlisberger following the Pittsburgh Steeler quarterback following the recent string of accusations of sexual assualt (particularly a 2010 accusation that led to his being suspended for the first four games of that season).
Stephon Marbury, he's either a selfish Jerk Ass who destroyed the Knicks organization, or a guy who was vindictively, blackballed and railroaded because of his testimony at a sexual harassment case that was leveled at the Knicks organization (which damaged their case). Or all of the above..
Fans of the Houston Rockets have been having a civil war for a long time now over star Tracy McGrady. His defenders say he's a hard-working player who battled through injuries, was forced to have major surgery, and then after working extremely hard on the rehab has been benched due to their vindictive coach or GM. His attackers view him as a selfish media hound who puts himself before the team, has been faking his injuries for the last 2 years, and is no longer part of the new star-less system created by their brilliant coach and GM that has done wonders for the team. And then we don't even get into the GM, Daryl Morey, who has been bringing the "Moneyball" approach described below into basketball.
Prepare to run from the chaos that will ensue if you say Alexander Ovechkin is better than Sidney Crosby, or vice-versa.
This seems to be dying down since it looks like while Alex is good, Sid before his unfortunate concussion was clearly surpassing his famous rival.
Kimbo Slice for many mixed-martial art fans. Is he a real fighter, one from the street with no training who just had a bad run, or a hustler who scammed his way onto national television for a buck?
Tim Tebow for NFL fans. His outspoken religiosity tends to be a Base Breaker. His abilities as a quarterback even more. Although he led the Denver Broncos to some amazing comeback victories in the 2011 season, his (in)ability to pass well has sparked much criticism.
Although his fans and detractors at least seem to agree that the Tebowing phenomenon is highly amusing, and it has become one of the first major memes of the Internet age that isn't restricted to younger generations, but apparently enjoyed by all age groups in America. (for any Europeans reading this, do a Google image search for Tebowing, you'll see what we mean).
He continues to be this, despite being the backup quarterback for a team that missed the playoffs last year; during preseason, the New York Daily News was publishing his statsfrom practices, apparently just so people can argue about him.
The Jerry Sandusky case has done this to Penn State's football fandom, particularly when anything related to Joe Paterno comes up. However, the pro-Paterno faction appears to be the most vocal.
Jay Bouwmeester brings turns Calgary Flames boards into rubble at the mention of his name. He was hired as player that was expected to take the team over the top, but in a league where 50% of the teams qualify for the playoffs, have even failed to do that in his tenure to date. Combined with a low intensity personality and a big paycheck, and the ongoing conflict of him being a capable player on a bad team or being dead weight has nearly brought entire forums to their knees.
Lolo Jones: Fans of track & Field either think she's a media darling because of her great personality, or it's because she's But Not Too Black, Ambiguously Brown and attractive. Also bring up how the media overly profile her at the expense of her other team mates, whom some believe is more deserving of the attention.
Compare her to Anna Kournikova (or Kimbo Slice) For Massive Damage, which by the way is not a complement.
Some would justify her media coverage due to the fact she has personality and is media friendly. But that within itself is controversial. What's more important looks and personality? or skill? Ideally both but her popularity seems to primarily be based on her looks and charisma more so than athletic ability.
Australian Rules Football, amongst Essendon fans: Is Kevin Sheedy the greatest coach in the history of the game, or an overrated, self-hyped man who should have won more premierships than he did?
For whatever incomprehensible reason, fans of The Beautiful Game absolutely adore getting into online flame wars about whether to call it "soccer" or "football".
And in real life, too.
John Oliver: When you call the sport by that name [soccer], an Englishman dies.
Arsene Wenger: a manager doing the best he can with limited finances, or a stubborn manager who has focussed on his youth policy to the detriment of the team?
After the groundbreaking transfer of Mesut Ozil, however, he seems to have broken the image of "stingy old man" for most people.
Manchester City (and before that, Chelsea): Teams just doing what's necessary to compete with Manchester United by spending bucketloads of cash, or ruining The Beautiful Game by distorting competition?
Who is the greater/more iconic English football team: Liverpool or Manchester United?
The Premier League: The best league in the world that provides thrilling entertainment, or a cash cow that has spoiled the game, concentrated the trophies in too few hands, and that the lower leagues represent "proper" football?
Barcelona: One of the best sides of all time that provide brilliant entertainment or diving, whining cheats that aren't really that exciting anyway because they just pass it without actually doing anything with it?
Stoke City & Tony Pulis: Practical, pragmatic tactics that allowed Stoke to stay in the Premier League, get to a cup final and qualify for Europe, or dire, dull and dirty?
Not only discussions about whoever is the best player in the world today (Messi, Cristiano Ronaldo, Neymar...) get heated, but you can expect the mention of the "greatest of all time" Pelé (or the nearest contestant, Maradona), and discussion on if the player being defended is better than him.
The animosity between rugby union and rugby league have been going on for over a hundred years, with league supporters accusing rugby union elitist, and union supporters calling league a game for "criminals and northerners." While the vitriol has decreased somewhat since the professionalization of rugby union, the debate shows no signs of going away.
In Gymnastics, the debate usually is Russia vs. USA. On Tumblr, saying you like the American team better is pretty much a death sentence.
In Rugby Union, the New Zealand All Blacks' performance of haka before each game. Some fans believe that it's a great spectacle that adds to the contest, while others say it is "barbaric" and gives the All Blacks an unfair psychological advantage. Other teamsnote national teams of pacific island nations, the Maori All Blacks and New Zealand's national female rugby team the Black Ferns also do a similar performance before the game, but the All Blacks' one is by far the most controversial, because they are the #1 ranked team in the world and therefore get more attention.