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I'm standing on a patch of grass in the infamous Lot 13 of the Home Depot Center, as Julio Ramos, the unofficial Chivas Mayor and core member of the Union Ultras, towers above me, talking about his love for his team. Somewhere off to the left of us, on the other side of a hedge that functions as a ceremonial divide between supporters groups, the Black Army 1850 are firing up the grill for their pre-game party. To our right Julio's fellow Ultra, the self-styled "Rey Misterio", is folding "Anti-Galaxy" scarves and unpacking a beer cooler for the Ultras' own pre-game ritual. Behind us, a temporary stage has been set up and a young dance troupe are performing a routine to a Jay-Z track, as a crowd yells them on.

Julio ignores the chaos as he tries to explain what Chivas USA means to him, as someone raised in a Mexican family with ties to Chivas Guadalajara, and who is now raising a family himself in the Los Angeles epicenter of the Southern Californian immigrant experience. As he talks, numerous kids are swarming off to the side of us in a tactic-free pursuit of a luridly colored ball. It ricochets dangerously close to the Ultras beer cooler and Misterio glances up sharply. The kids look wholly unperturbed – the atmosphere at the Ultras pre-game tailgating is utterly unthreatening – the heat, the collegiate setting, the lawns and flower beds make this feel like a slightly boozy high school graduation party. Julio watches the scene indulgently. I ask him how he got his honorific of Chivas Mayor and he shrugs: "Everybody knows me round here. Everybody knows the passion I have for the team – for me it's not a team, it's a religion."

Palm trees outside the Home Depot Center - shared home of Chivas USA and Los Angeles Galaxy. Photograph: Graham Parker

You need a special kind of faith to be a Chivas USA supporter in Los Angeles - let alone MLS. As our regular Chivas previewer for the Guardian, and editor of The Goat Parade blog, Alicia Ratterree puts it:

What is it like to be a Chivas fan? To me, Chivas USA don't like jumping on the bandwagon. They like an underdog, and have a bit of a contrarian streak. They have to put up with a lot of abuse from opposing fans, so they are tough. How many fans in MLS are told their team is a "failure" and that the club needs to fold? Only Chivas.

Leaving aside the difficulties and hang ups of sharing a stadium with the wealthy and (last season at least) all-conquering LA Galaxy side, Chivas USA arrived in the league too late to be one of the MLS originals, or near-originals, like today's opponents Chicago Fire, and too early to ride the wave of supporter-culture that characterizes the current success stories of MLS 2.0 sides such as the Cascadia teams of Portland, Vancouver and Seattle. As I talk with Julio, he is quick to acknowledge there have been mistakes and that other sides seem to have reaped the benefit of the lessons, but he is resistant to the idea of Chivas as a cautionary tale. He's also insistent that all that is needed is for the team to do a better job with telling people who they are. It begs the obvious question, who are they then? Julio becomes animated by this:

Listen - Chivas USA, to me, is a team that represents the American dream for all the immigrants, because Chivas USA represents the pueblo. El pueblo is like the main hardcore people of Los Angeles - which are people from Mexico, Puerto Rico… everybody – all the immigrants that come to the United States. Because that is what the name Chivas USA is telling you – we all came to live the American dream. Chivas USA represents all of those people, hard-working people, where the only thing we want is to succeed and to give our best to this country and honor Chivas in this league.

As we talk more it becomes apparent that his sense of how best to honor that identity is a complex one – Julio is somewhat critical of the team's original public statements, emphasizing a Latino selection policy, that characterized the team's entry into the league (and which were, predictably, quietly abandoned as the expansion side began to deal with the real-politic of operating within the roster restrictions of MLS). Now, he says, the fans just want the best team on the field, whether they're "Latino, Asian, whatever…".

To a supporter of any other side in MLS, such a statement would be a no-brainer, but such is the life of a Chivas USA fan - both proud of, and somewhat inhibited by, the legacy of parent team Club Deportivo Guadalajara. Historically, Guadalajara are the most successful team in Mexican soccer (notably, the club crests of the two sides are replicas, but for the 11 stars, for 11 national championships, that adorn Guadalajara's badge...), built on a legacy of exclusively using players of Mexican origin. When their 'little brother', Chivas USA, entered MLS in 2005, they brought that legacy, a recognizable brand, even a branch of the Guadalajara supporters club - but they also carried a weight of expectation and an identity that hasn't yet fully translated to the local market and the contingencies of the emerging domestic game in the USA and Canada. What has happened though, is that supporter groups like the Ultras and the Black Army have taken shape - groups that try to support the team in the specific context of their existence in California and MLS, rather than as an imitation of another team that suffers by comparison. Many (most) are Guadalajara fans too, but have thrown themselves into celebrating their local team. And in celebrating what they have, rather than what they lack, they've found a voice.

Later, I speak by phone to Angel Mendoza, the President, and one of the original 11 founding members, of the Black Army 1850, and he is adamant that their group is about reflecting "the melting pot of Los Angeles" before any historical loyalties:

We love our heritage - I'm Mexican-American myself...but we want the team to grow here in LA, to be a staple of the game in the United States... As long as you're supporting our Goats - we don't care if you're Russian, German, Irish, Mexican, Brazilian, Argentian - just stand with us.

Born in Mexico City and growing up a Pumas supporter - Angel has been in California since he was six years old. Unwilling to follow the Galaxy when they first appeared ("I just wasn't into them and wasn't willing to just go with an LA team just for the sake of it") he's critical of Chivas USA's original and continued attempts to market the team primarily to the Hispanic community:

When you're hitting that market - you're basically shooting yourself in the foot. You have the Guadalajara fans, who look at us like the copycats who really don't matter; you have the Mexican-American fans who already have deep roots in Pachuca, Pumas, whatever, and they have a hatred towards the colors; so you're already eliminating half your market - you know, what's left? And that's where we come in...It's the 21st century - we're proud of being here in the US. I have two little girls and if they play soccer when they get older, they're going to play for the US Women's National Team. I have to help the sport grow here.

Chivas USA super fan 'Rey Misterio' of the Union Ultras at a pre-game party at the Home Depot Center. Photograph: Graham Parker

So what of the team right now. I ask Julio what he thinks of the current incarnation of the side. He's impressed by Coach Robin Fraser's eye for a player, but less impressed by his conservative style of play ("We addressed the defense already. Believe in them. Believe in Kennedy…let our guys attack"). But he sees lots of positives in the squad: The excellent keeper (Dan) Kennedy, of course, and captain Oswaldo Minda, but also "Smith, Riley, The Columbians, Moreno...we have talented players. They just..."

He tails off. There's an undercurrent of anxiety before this game. Chivas go into it having lost each of their four opening home games 1-0, yet with puzzlingly good away form - though those who see Fraser's defense first approach as a problem sometimes point to the fact that the side looks unsure of themselves 'leading the dance' as a home side, whereas his cautious invitation to other teams to break them down, can suit his team on the road. As it turns out they will take the lead tonight through a Juan Pablo Angel penalty, only to instantly concede an equalizer and a devastating Marco Pappa winner in stoppage time. But as the pre-game partying and back-slapping continues, that reality is still in the future.

Also in the future is the first SuperClásico of the season against their Galaxy "room mates" at the Home Depot Center. Both sides have struggled at home all season - Chivas with their litany of tight home defeats, Galaxy with a series of unexpected losses to Toronto, Real Salt Lake, New England and New York, to leave last year's unbeaten home record in tatters. By default this may be the closest contest between the two in years - since Chivas beat the Galaxy 3-0 twice in a delirious three week period in 2007, on their way to the Western Conference title, the Galaxy have won or tied every competitive game between the two - a period roughly coinciding with the Galaxy's media presence heading into the stratosphere in the Beckham years. You could understand the Chivas fans being bitter, and the Anti-Galaxy scarves suggest there's something to that, but Rey Misterio insists it's all done in humor and that while the rivalry is real, the Ultras have respect for some of the other fan groups:

You know what? We actually have a pretty friendly relationship with ACB (Angel City Brigade - now the largest Galaxy supporters group). But, you know, it's a friendly relationship when we're in the parking lot. We're having a beer and everything's cool, but once we go inside the stadium we hate each other the same way!

That particular friendly rivalry will be tested just prior to the SuperClasico (an adaptation of the El Súper Clásico nickname given to the clashes between Club América and Guadalajara), when members of the Union Ultras and Angel City Brigade will meet in their own BarraClasico game prior to the main event (The LA Riot Squad will also face off against the Black Army 1850 group). For now there are other rivalries to deal with. Looking over Rey's shoulder I notice a couple of Chicago Fire shirts who turn out to be familiar faces from the Section 8 supporters group who've arranged to meet up with the Chivas fans to tailgate before the game.

The Ultras party is well under way now - the 'Mayor' is circulating and Rey is in animated conversation with other members of the Ultras. I wander round to the Black Army side of the hedge but get waylaid and end up talking with the Section 8 guys, including their current events director Josue Gomez and original Section 8 chairman Marcin Tłustochowicz. The latter helped found one of the original Fire supporters groups, Fire Ultras, in 1998, alongside several other Polish ex-pats in the city. I ask him if he finds it unusual to be hanging out with the hardcore of opposing fans on game day and he says that on the contrary, he really appreciates "people who are into building that still fragile...ecosystem. You have to understand that there are very few of these people - and they are completely altruistic in what they do."

We talk some more about the history of Section 8 and its dizzying array of sub-groups, who somehow manage to come together to get things done, despite what Marcin jokingly calls the "Balkanization" of the support. He speaks with pride, without boasting, of Section 8's role at the forefront of the early TiFo displays to appear in MLS. We talk about his Polish roots and the passion for the game bred there - unlike Julio he doesn't want to describe it as a religion, but does say wryly that maybe he and his friends are like "Buddhist monks chanting their mantras" - it led to culture clashes and misunderstandings in the early days of their appearance on the MLS scene, he says. Opposition security teams didn't know what to make of their raucous presence and treated them as "the root of all evil." It's better now, he says, gesturing at the cheerfully indifferent Chivas security - "for the most part..."

I look past Marcin to where the dance troupe is finishing up their routine. As they clear the stage, the backdrop is clearly visible - a photo of the LA skyline emblazoned with the Chivas USA crest and the single word "Belong". Whether it's Marcin's generosity about his fellow supporters, or Julio's impassioned speech on the importance of Chivas for El Pueblo of Los Angeles, or just my own strange journey to living in this country and following MLS, from an unlikely start in Belfast, I find myself affected for a moment by the sight of that word (even as I'm berating myself for falling for a marketing slogan...). Just about everyone who has followed MLS up to this point has probably done so with a heightened sensitivity to what it means to 'belong' - at the very least to a sporting sub-culture that at times has clung on by its fingertips in this part of North America. As we move deeper into season seventeen, and kids who've never known a time without MLS potentially start to enter the league as players, and TV networks push ever more global soccer onto US screens, an earlier evangelical fervor about belonging, on the part of that first generation, will inevitably become something else for those that follow. It'll definitely be bigger - watching the people around me, I can't imagine it will be better.

Graham Parker is a regular MLS correspondent for the Guardian.

Part two of this story - focusing on LA Galaxy - can be found here.

Join Graham for minute-by-minute coverage of Chivas USA vs. Los Angeles Galaxy this Sat 19th May 10.30pm, here on the Guardian.