Time to step it up, heavy-metal fans. Country music concertgoers raise more hell than you do.

That’s the recent experience of Craig Baltzer, general manager at the Idaho Center. The Nampa venue will host a headbanger gathering July 4 called the Mayhem Festival.

Baltzer doesn’t sound worried in the slightest.

Strange. This year’s co-headliner at MayhemFest is Slayer, a quartet who is not a fan of barbershops.

Slayer’s breakneck-speed singalongs are filled with fun choruses such as “Ripping apart/severing flesh/gouging eyes/tearing limb from limb!”

Slayer fans may look a bit rugged with their ratty hair, pierced eyebrows, black T-shirts, tattoos and machetes.

(OK, just kidding about the machetes.)

But, shucks, these MayhemFest concertgoers have mommies just like the rest of us.

“It’s really amazing,” Baltzer says.

Not the mommy part — although that fact is pretty crazy when you just look at some of these fans.

Baltzer is talking about the behavior evolution of concertgoers.

A couple of years ago, Baltzer read an article claiming that problems had decreased at rock shows but grown at country events.

So Baltzer started paying attention in Nampa. And guess what?

It appears to be true.

“It’s an interesting thing,” he says. “I’ve brought it up with other people in our industry. Everybody agrees.”

Last year, the Idaho Center hosted Tim McGraw in June. Baltzer remembers three or four arrests, 11 or 12 ejections and three “major medicals” — meaning someone had to go to the hospital.

A few weeks later at MayhemFest? One arrest. Two or three ejections. One major medical.

A decade ago, you could have expected five times that many problems at that type of event, he says.

“Mayhem’s an all-day festival,” Baltzer says incredulously. “Literally eight hours of rock ‘n’ roll, multiple stages, 7,000 or 8,000 people there.”

Sounds like a recipe for disaster. But it’s not.

“For the last two Mayhems I’ve seen, it’s been a very easygoing, polite audience there to enjoy the music and have fun and drink,” Baltzer says.

“And, boy, do they drink beer!”

Ahem.

“We sell a lot of concessions, let’s put it that way,” Baltzer adds, tempering his enthusiasm for this yearly money maker.

Hard liquor is even sold at MayhemFest. Incredible.

Baltzer isn’t sure why the metamorphosis has occurred. Why cowboy-boot-wearing fan has become more rowdy than skull-shirt wearing dude.

Age could be a factor, he says.

Country music has done a good job of attracting younger fans in recent years. Metal and rock? Well, a lot of those fans just keep getting older.

Making trouble takes a lot of energy.

Still, MayhemFest is happening on the Fourth of July this year. Heshers will tailgate for hours before they stumble into the amphitheater.

Come on, Mr. Baltzer. You just know there’s going to be an M-80 firecracker exploding right in your face at some point at this festival.

He laughs in acknowledgment.

“Something’s gonna happen, right?”

FUN RETURNS BEHIND 13TH STREET PUB

Hyde Park ’Til Dark is back — sort of.

The outdoor concert series behind 13th Street Pub & Grill was canceled abruptly last summer after a North Ender complained to Boise police about noise.

But on June 23, bands, beer and barbecue returned. It was the grand finale bash of the Pedal for the People bicycle celebration.

Man, was it fun. (Apologies to the splattered victims of my shirtless, maniacal 2-year-old moshing in the puddle.)

Bands including Boise acts Atomic Mama and Dedicated Servers performed. Bicyclists dueled in games of chicken in a circle marked on the concrete.

All of Hyde Park seemed energized by the Saturday-night social gathering.

Mike Morrison, co-owner of 13th Street Pub & Grill, says he decided to try live music again because: 1) It was for a nonprofit group, Boise Bicycle Project; 2) Organizers canvassed a larger area in advance to warn North Enders about the music noise.

This time, the stage also was equipped with walls on each side to help channel sound forward.

“We didn’t hear a word about anything (from neighbors),” Morrison says. “So it was great.”

Morrison isn’t ready to relaunch an outdoor music series just yet. But he is considering one more concert this summer. A brew festival around September also is being kicked around.

Why not? It’s tough to beat a party in that parking lot.

“The atmosphere,” Morrison says. “People are just loving that.”

TONIGHT IN 94.9 FM’S ‘THE OTHER STUDIO’

Co-host Tim Johnstone, will appease me by listening to Slipknot and Slayer. We’ll welcome members of Boise metal band Karin Comes Killing into the studio. Plus, we’ll play new music from Shawn Colvin and old music from Boise Music Festival headliner LL Cool J.

And talk a lot. As usual.

“The Other Studio” airs from 9 to 10 p.m. Sundays on 94.9 FM The River.

COMING JULY 6 IN SCENE

Æ The massive Boise Music Festival moves to Garden City. Will it be quite the same?

Æ Oliver Stone’s crime-thriller hits movie theaters.

Æ Casting with the family-friendly Woolly Buggers fly fishing club.

Michael Deeds’ column runs Fridays in Scene and Sundays in Life. Email: mdeeds@ idahostatesman.com. Follow him on Twitter: @IDS_Deeds