The 10th annual HFStival was billed as an all-day rock concert, but it seemed more like an Iron Man competition with background music tossed in. Attendees broiled and jostled for space in a packed stadium like runners in the opening mile of a marathon. But it was alternative rock itself, now in the throes of a midlife crisis, that was sweating more than anyone.

Saturday's endurance fest at PSINet Stadium, home of the Baltimore Ravens, featured about 30 acts on three different stages, including such alternative rock perennials as Red Hot Chili Peppers, the Offspring, Goo Goo Dolls, Live and Sugar Ray. A sell-out crowd of 75,000 and then some was on hand to pogo, mosh and hunt for a decent restroom.

"Where else can you go see this many bands for $25?" asked Henry Harding, a well-pierced 24-year-old Washington bartender.

Nowhere, is the short answer. Still, this year's celebration of alternative rock arrives at an awkward moment for the genre, which exploded in the early 1990s by marrying fat, crackling guitars to punk attitude and lumberjack flannels. The flannels are long gone by now, but so is much of the sparkle and freshness that made the music seem so joltingly alive when Nirvana's Kurt Cobain first strapped on a Fender Mustang guitar and sang about the smell of Teen Spirit.

The problem isn't merely that success has made the "alternative" tag seem a little silly. You can start scribbling the obit of any musical movement when its heavyweights hew to a formula rather than reinvent it, and for a few years, alternative rockers have been been producing play-it-safe records that sound uncannily like their previous offerings.

Meanwhile, hip-hop and rap have been eating alternative's lunch, and the sugary teen-idol confections of Backstreet Boys and Britney Spears have commandeered the charts. Which is why some stars of Saturday's show sounded at times like doctors who'd come to diagnose a near-terminal patient.

"It's been a little barren," said Edward Kowalczyk, the lead singer of Live, in an interview. "It seems like there was a great upsurge of stuff in the early '90s, and then there was a lot of stuff that seemed to sort of ride the wave, that wasn't to me as important or seemed more copycat. And there was just so much of it, that it felt like, where did it go, you know, what happened?"

Moby has a guess. The 34-year-old techno maestro and deejay, who spun records during a main stage cameo, pinned the blame for alternative's woes on corporate overlords at major labels, who worry first about their shareholders and prod artists for sure-fire hits.

"Alternative rock was terrific when Nirvana broke it open in the 1990s," he said. "But in the interest of making the music more commercially viable, record companies and artists have really compromised the creative integrity of the music."

And what about alternative radio? Once a bastion of the new and the untested, play lists at stations like WHFS now tilt heavily to the old and the pre-approved. Listeners would need the luck of a deep-sea treasure hunter to spot some of Saturday's performers, like Ozomatli and the Living End, on the radio these days.

"It's a tricky situation," said Moby, trying hard not to insult his hosts. "The marketplace realities are what they are. It's just a shame when integrity gets sacrificed so extremely along the way."

Still, if the genre is out of innovative gas, it's lost none of its onstage energy. This HFStival was low on unscripted weirdness, like the moment a few years ago when Jewel skulked off stage after getting nailed by a heat-seeking Frisbee. But the scripted stuff was impressively passionate.

Live tore through a greatest hits session focused heavily on its 1994 smash album, "Throwing Copper." Sugar Ray's lead singer, Mark McGrath, dedicated the band's hit "Fly" to his recently departed grandmother and took a nifty potshot at the Ravens by wondering aloud if the team is part of Canadian Football League.

The Offspring came up with the day's most inspired vaudeville, calling an intermission in the middle of its 45-minute set and then plopping into onstage seats while an overweight man in a red G-string led the crowd in a group wave. The band also stirred the day's biggest mosh pit, an impressive 40-square-yard scrum of sweltering teens pushing and passing one another overhead.

Red Hot Chili Peppers owned the evening's coveted last slot, and they earned it with a funk and punk retrospective that opened with "Give It Away." Bass player Flea introduced "Scar Tissue" with slap at the teeny-bopper acts that have been muscling into the prime real estate on bestseller charts, calling the song the work of the "brain trust of the Backstreet Boys and 'N Sync."

But PSINet Stadium isn't exactly an ideal place for a rock concert. This was the HFStival's first year there, after years of holding the show at RFK Stadium. While the venue is unquestionably larger and spiffier, its acoustics are no improvement. In the middle of the stadium, the music sounded as tinny as AM radio at full blast, and anyone sitting at the end opposite the stage heard a kind of muddled, musical pudding.

"It started out really good during the Mighty Mighty Bosstones," said Rich Madow, a 40-year-old dentist who described himself as the oldest guy at the show. "But by the time Sugar Ray came on it was a distorted mess."

And let's face it, any stadium is a pretty lousy place for a rock concert, which needs the intimacy of a small space, darkness and perhaps a roof to pack maximum wallop. Most fans either watched the show on the end-zone screens or wandered out of the stadium and into the makeshift food court in an adjacent parking lot.

Apparently kids today believe there is no better way to cool off and recuperate from sunstroke and hours of dancing than to bite into a foot-long slab of meat courtesy of Ostrowski's Polish Sausage. For others, it was a Philly cheese steak, some boardwalk fries or the offerings of Beefalo Bob's.

Others treated themselves at the Grafixx Tattoo and Body Piercing booth, where a line of teens waited to enhance nature's own handiwork by plunging silver rings through their bellybuttons and nipples--at $40 a plunge.

There were countless other booths, promotions, pitches and assorted come-ons from clothing makers, car insurers, Internet providers--the list goes on. The unabashed commercialism seemed fitting somehow. A decade ago, the HFStival had the subversive feel of an underground movement, a place to showcase music so resolutely raw that it seemed to catch on despite itself. Now even alternative rock's bigwigs are fretting about the need for a new musical Moses, and the event is all but overwhelmed by its sponsors.

"It's all about the beer," read a Heineken ad towed behind an airplane that circled the stadium late in the afternoon. By then, you had to think, well, maybe they've got a point.

CAPTION: Head over heels at the HFStival: Johanna Jonsheden and Aaron Zimmerman kiss, top; and moshers get physical Saturday at PSINet Stadium in Baltimore.

CAPTION: Ryan Shuck, above, lead guitarist for the Orgy, performing at the HFStival in Baltimore Saturday, has a, er, mesmerizing effect on at least one audience member, Ryan Moses.