AMSOIL Arenacross dirt bike racing at the Baltimore Arena is enjoyed by all ages. Kids as young as 4 years old compete for prizes. (Baltimore Sun video)

Seth Wallace knew early on he wanted to race dirt bikes, just like he saw on YouTube.

He's only 5, but the youngster from Nicholson, Pa., got his wish Sunday as one of 314 riders ages 4 and up to take part in amateur day at a weekend Arenacross event at the Baltimore Arena.

In a series of races, up to 16 riders at a time bolted from the indoor dirt track's starting gate on motorized bikes, then fought for a clear path ahead. Kicking up dust, with engines roaring, they sped around hairpin turns, negotiated bumps and soared over hills. Occasionally a rider wiped out, then scrambled up while avoiding others flying by.

Seth, who started racing last spring, "came to me one day and said he wanted a dirt bike," said his father, Robert Wallace. "He's really into it."

The popularity of the indoor version of motocross is growing as extreme sports become more mainstream and kids follow their parents and even grandparents into the sport, said Bill Heras, the arenacross event manager for Feld Motor Sports. The company owns Amsoil Arenacross, featuring Ricky Carmichael's Road to Supercross, which runs professional and amateur events in 12 cities during the winter season. Baltimore's indoor track took two days and 150 truckloads of dirt to build.

"This is the grass roots of the sport," Heras said.

Some competitors travel the circuit of cities in their region, loading up bikes and gear into vans and pickups. Many aim to rack up points in each event by placing fifth or better in one or more of the 25 races, classified by age, skill and bike size. High scorers can qualify for an amateur championship event each May in Las Vegas. It can be a hefty investment. Riders said new racing bikes can cost around $4,000, and many keep a second, used bike for practice, not to mention helmets and other protective gear that can add hundreds more.

It's all worth it to Troy Smith, 20, of Brandywine, who placed fourth in his class Sunday. Smith, who works in maintenance for the State Highway Administration, started riding at age 5 then began competing seriously five years ago.

"I just love the adrenaline rush," Smith said. "I love to go fast, with everyone screaming at you. I like to be a competitor. I want to be known as the guy to beat."

Tami McLaud, of Cedar Rapids, Iowa, spends weekends each season driving her three sons, ages 17, 15 and 10, and their bikes in a van to events all over the country. Her eldest son, Brett, 17, has been racing since he was 4 years old and has placed in the national competition in Las Vegas.

He hasn't been deterred by injuries, including fractured vertebrae in his back.

"It goes along with the sport," he said. "If you crash, you crash. You want to get back up and keep trying."

Wallace, whose son Seth competed Sunday, said he worries about injuries but "that's why we spend a lot of money on good equipment…and teach them the right way to do things. He knows [the bike] is not a toy."

Steven Davis brought his son Parker, 6, to race in his first arenacross on Sunday. Davis, a plumber from Silver Spring, also competes, and his father attends the events.

The sport "is good for family bonding," he said. "It keeps the family together."

Ronnie Stallings, of Huntingtown, who competed in motocross events some 25 years ago, now coaches his 6-year-old twin sons, Dominic and Colton Stallings, who competed in their first race less than a year ago.

Stallings says before each of his sons' races, he wheels the small bikes to the starting gate, tells the boys he loves them, then goes over final pointers.

The most important one he saves for just before he steps away, telling them, "I don't care what you do, just be safe."

Lorraine.mirabella@baltsun.com