SIDELINE CUT: IT IS highly likely Giovanni Trapattoni will have noticed the vast exodus from Munster for the shindig over in Cardiff this evening.

The Italian may well have had some knowledge about the infamous border that separates the sons of Ulster from the rest of Ireland but he will probably be somewhat puzzled to learn about the cultural and sporting complexities that involve all four of our green fields. In fact, when he comes to understand the appetite for rugby in this country and, over the summer, learns about the kind of crowds and passion that the GAA championship commands, he might wonder what hope there can ever be for the garrison game here. But equally, he might look at the drive and phenomenal energy behind the Munster cult and, like the diner watching Meg Ryan in the restaurant, decide that he wants whatever they are having.

Imagine trying to explain what Munster are about to the Italian. We seem to have difficulty enough in grasping it for ourselves. In terms of sport, the traditional expression of Munster vibrancy has always been the hurling final and the deep-rooted and sometimes bitter rivalries that competition has created between the counties. Of course, the Munster rugby team always had a fine tradition through the interprovincial games and that historic victory over the All Blacks. But as the first generation of Munster professionals have often reminisced, Munster drew fairly modest crowds and were in the main an occasional team supported by burghers from the rugby enclaves of Limerick and Cork.

Few could have anticipated that the transformation of Munster into a full-time working club would generate such mass loyalty and support drawing on a vast cross-section of people from across all counties. It helps, of course, that Marcus Horan is from Clare, and Denis Leamy and Alan Quinlan hail from Tipperary, that the totemic figure of Mick Galwey emerged from the mists of Kerry and that Peter "the Claw" Clohessy was notionally born in Limerick but was in fact a gift from Thor, the god of thunder.

It helped despite the perception rugby is a game for posh lads, the Munster rugby team seemed wedded to the kind of blue-collar values found in the lyric sheets of a Bruce Springsteen album. When it came to turning professional, the club were enormously lucky to have men of the calibre of Anthony Foley, who once proclaimed he would be happy to drive a school bus for a living whenever the glory days were over.

Whether by accident or design, the first generation of Munster players managed to devise a principle whereby they held huge notions about what they could achieve as a team but very few notions about the notion of individual stardom. And it mattered that the foreign players they recruited seemed to understand this mindset and bought into it, with Jim Williams being the most obvious example of an adopted Munster man.

Many foreign players have spoken of their initial bafflement at the whole Munster set-up. It took them a while to cotton on to what it is that makes Munster different. Here was an ambitious, highly organised and handsomely funded professional team that had somehow managed to cling on to the best virtues of the amateur tradition - the humour, the camaraderie and that innate Irish quality of taking on the world.

Slowly but surely, tens of thousands of people living in Munster began to see something in the rugby team that they liked. It is easy to get a little sniffy about these arrivistas hopping on what even Munster's most admiring television pundits unabashedly describe as "the bandwagon".

For Irish people unfortunate enough to be living outside Munster, there were times when the radio and television men insisted we all but genuflect in front of the Red Army. That is particularly galling for Leinster rugby folk, who can console themselves only with the fact they score a silkier class of try and can choose from a more lavish range of nightclubs.

Munster folk carry on regardless. For well over five years now, people have been putting their money where their mouths are, travelling to follow a team that suffered several tough defeats before realising the ultimate glory. And the mass travelling support guarantees Cardiff will have an overwhelmingly Irish flavour this evening.

What is clear is that for supporters, Munster are an equal opportunities team. True, they attract the archetypal rugby chap from the leafy 'burbs - the silver-haired executive still in touch with the lads from the class of '54 who likes his Vivaldi loud and jokes blue. But at Munster games he will stand shoulder to shoulder with students, farmers, eco-warriors, hurlers, hippies, GAA stalwarts, soccer aficionados and the cast of characters who inhabit Pat Shortt's little ditty, Breakfast Roll. I even know one Beatnik-type lad who won't be seen dead in anything other than a John Hayes replica shirt at this time of year.

Maybe in years to come, the sociologists will decide the Munster phenomenon was down to people needing to identify with a big-hearted and inclusive movement at a time when there was a dearth of such churches. Or maybe the reason for the huge groundswell of feeling will be attributed to the old saying that we are here for a good time, not a long time. When Munster are pitted against Leinster, the opposing values are reduced to country versus city. But it can't be that simple: Cork city folks can visit New York and express their delight they have jazz and a City Hall over there as well. There are plenty of self-respecting cosmopolitans in the Munster brigade.

No, the thing about Munster seems to be that they represent whatever their people want them to represent. The magic of it is that they defy categorisation. As the famous line goes in Saturday Night and Sunday Morning, "Whatever people say I am, that's what I'm not because they don't know a bloody thing about me." All that defiance and independent spirit and the classic us-against-the-world ethos surges through the Munster teams for reasons that seem mysterious even to themselves. And from the team, it beats through the crowd. In Thomond Park, they like the skies dark and soaked, the floodlights on, the air to be frozen and the beers to be tepid. No fancy stuff, as they say.

Even now, as Munster prepare to thunder for another 80 minutes of collective magnificence, it has to be asked how long it can all continue. Foley is due to bow out after this evening's match, another of the round-table men gone. Over the years, as the senior men depart one by one, it will surely become more difficult for Munster to preserve that sense of fun and privilege in the dressingroom and to commit to a cause in a way that transcends mere professionalism. The whole point of Munster is that they play for a cause and that is what brings people in. Who cares that we are not fully sure what the Munster cause is? It's like Marlon Brando's immortal response in The Wild One.

"What are you rebelling against, Johnny?" "Whaddya got?"