Fighting, of one form or another, is at the core of Southern California punk vets Pennywise. Although the band was founded on the principles of positive thinking and self-determination, over the past 25 years, its career has been defined by conflict, whether in its politically agitated lyrics, its tussles with rival bands or its occasional use of onstage vomiting as a form of protest. Three years ago, its own internal strife led to the departure of Jim Lindberg, the group’s frontman for almost two decades. So when new singer Zoli Teglas was told that, as part of his initiation into the band, he’d have to bare-knuckle box 6-foot-8-inch, 300-plus-pound guitarist Fletcher Dragge, he took it seriously.

“I called him one night before practice, and I was pretty drunk,” says Dragge in a groggy baritone, “and I told him that before practice tomorrow he had to fight me, Fight Club-style, and I was going to kick his ass. I wanted him to get dirtied up. I told him I was gonna beat the shit out of him, roll him around in the gutter, and give him some grit.

“He shows up the next day, and I’m hungover as fuck,” he continues, “and he shows up with a mouthpiece. I’m like, ‘Dude, we’re not really going to fight. I was just fucking with you.’ ”

It was an understandable mistake. Aggression is the fuel that’s kept Pennywise running longer than almost anyone would’ve anticipated. Emerging during the mid-’90s punk revival alongside fellow Epitaph Records alumni the Offspring, Bad Religion and NOFX, the band dedicated itself to a fast and furious, bottled-lightning mix of chugging guitars, bullet-train drums and fiercely melodic vocals. It has hardly meddled with that formula since.

On its last few albums, however, the group fell into a kind of stasis. It still sounded like Pennywise, but it didn’t feel the same. According to Dragge, it wasn’t age, even though he and the other core members, bassist Randy Bradbury and drummer Byron McMackin, are all hovering close to 50. The problem was Lindberg. With the singer seemingly always on the verge of quitting, the band had taken to tiptoeing gingerly around him, neutering the once-volatile creative process that produced fan classics like 1993’s Unknown Road and 1997’s Full Circle.

In 2009, Lindberg finally left — allegedly to devote more time to his family, though he soon formed the Black Pacific, a band Dragge calls “Pennywise as a one-man show.” (He and Lindberg are not currently on speaking terms.) Luckily, the band had a backup plan: It recruited Teglas, the forceful vocalist for Orange County hardcore mainstay Ignite. He made an immediate impact.

“With Zoli, it felt like we were back to the roots of Pennywise, where it was no holds barred,” Dragge says. “You just spoke your mind and didn’t care if you hurt somebody’s feelings.” That unfiltered line of communication carried over to the studio when the band went in to make its first record without Lindberg. “There was a lot of headbutting going on in the songwriting process,” Dragge admits. “[Zoli] is an alpha male. He was the shot-caller in Ignite, so he comes into Pennywise and starts telling us what we’re doing wrong, and what we need to do. And we’re just like, ‘Twenty years later, I think we got a handle on this.’ ” But the pushing and shoving paid off: The recently released All or Nothing sounds like a band revitalized. It’s got the speed, the anthemic choruses and the grip-tight playing fans expect of Pennywise, with the added charge of a band that, after a half-century together, suddenly finds itself with something to prove.

And it still does have something to prove: Most bands don’t recover from losing their longtime singer. Discussing the challenge of convincing skeptics that Pennywise is still vital, Dragge — unsurprisingly — uses the language of battle.

“We’re in a struggle right now. We’re fighting for our lives,” he says. “This isn’t over.”

Pennywise will perform at the Ventura Theater on Friday, May 11. Guttermouth will open. See