Running then became something that brought back tragic memories.
As a refugee in the United States years later, he made a discovery: He was good at running long distances, and he could run them fast.
The Sudanese marathoner was to board a plane from Arizona on Thursday bound for London, where he will compete as an independent athlete at the Olympics. A runner without a country to call his own, he hopes he can use his Olympic moment to become a symbol of hope.
Marial qualified for the Olympics last year while running his first-ever marathon, but he couldn't compete for the United States because he's a permanent resident but not yet a citizen. He learned just weeks ago that he'd be able to compete, running under the Olympic flag. He turned down an offer to run for Sudan because he couldn't fathom representing a country in which so many Sudanese have suffered, including his own family members, and from which he fled as a boy. His native South Sudan — the world's newest country — doesn't have an Olympic team.
Marial isn't expected to win but that seems to matter little to him.
"I'm running for the support of the United States, that people of the United States will support me, who helped me, who show me this sport, who brought me here," the 28-year-old Marial told The Associated Press while training in Flagstaff. "I'm running for the refugees and I'm running for the South Sudanese, especially."
The marathon isn't an event in which Marial has much experience. His finished his first-ever 26.2-mile event, the 2011 Twin Cities marathon, in 2 hours, 14 minutes, 32 seconds — an Olympic qualifying time.
He knows he's not favoured to win a medal but has strong determination to do the best he can considering the circumstances.
"Unfortunately the time is not enough on my side do more quality (runs) in time for the Olympics," he said.
The International Olympic Committee cleared him last month to compete in the Olympics as an independent athlete after he didn't qualify for Sudan, South Sudan or the United States under its rules.
Marial trains amid the cool ponderosa pines of northern Arizona, in a community with a history of being a training ground for other elite runners. He was drawn to the city that sits at an elevation of 7,000 feet and has relatively cool summers while attending college at Iowa State. Flagstaff, which also was a training base for Olympic marathoner Ryan Hall, has been his home for the past year.
Beads of sweat ran down Marial's face, his knees reaching up to the sky as he exploded over hurdles, during one of his final training sessions before London this week. He had planned to squeeze in another workout Thursday — a 12- to 15-mile run — before boarding his flight to the Olympics.
Marial wasn't set to compete in another marathon until October in Chicago, so he quickly changed up his training regimen to include more quality runs.
He spends hours a day in the gym and on the trails and tracks in Flagstaff, alternating shorter, strength-based workouts with longer runs in which he's upped the tempo since learning he'll be an Olympic athlete. He has set aside his job at a group home to focus on running.
His journey has been anything but easy. When he was a child, he ran under the cover of night to escape a life of slavery. He was kidnapped by gunmen and forced to work. More than two dozen of his family members died due to violence or disease during the civil unrest that devastated the country and led to the breaking away of South Sudan last year.
"I myself was in danger. I was beat up, they broke my left jaw, and they broke my auntie's — my uncle's wife's — collar bone," he said. "So we were taken to (the) hospital."
An emergency that he didn't want to discuss cut the hospital stay short, and Marial eventually made it to Egypt and to the United States. His father still lives in South Sudan.At 16, Marial joined the Concord High School track team in New Hampshire, with the encouragement of a gym teacher who saw he never got winded during any sports activities in class. He graduated in 2005, earning a scholarship to Iowa State in Ames, Iowa. He became an All-America in cross-country his junior year.
Marial hasn't posted winning times, but that seems to matter little to him. Running in the Olympics gives a voice to the South Sudanese, he said, and highlights the country's spot in the world community.
In Flagstaff, others on the soccer field watch unaware of what led Marial to the mountainous city and of the next leg of his journey. Training in Flagstaff has allowed him to improve on his initial marathon time by two minutes.
"The best runners come up here," he said. "As a marathoner, this is a place that success would come."