SANTA MARIA, Calif. — The boxer dances across an empty ring, moving to a beat only he can hear. His punches snap with a grace honed by years of hard work.

All the times he rose early as a boy, running cold streets while classmates watched from a passing school bus, made him quick. All the times he trudged across town, lugging a duffel bag full of gear, made him strong.

Carlos Balderas remembers wanting to skip workouts. "Growing up, I had friends and they always hung out," he says. "My dad made me go to the gym."

His father watches from outside the ring and recalls how a skinny kid grew into a powerful 19-year-old lightweight who will box at the Summer Olympics in Rio de Janeiro next month. Zenon Balderas insists it took a stern hand to bring out the best in Carlos.

Yet there is doubt in his voice.

"Was I too tough?" he wonders. "Sometimes I feel bad."

This converted warehouse buzzes with young fighters skipping rope and pounding the heavy bags. Carlos _ his arms glistening with sweat _ has the ring to himself.

Tears well in his father's eyes.

Zenon says he pushed his son hard for a reason. He talks about a family that made its way up from Mexico to work the strawberry fields of Southern California. He talks about surviving.

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The Balderas home was overflowing with a dozen or so bodies squeezed into two bedrooms. Still, Emiliano drove to the city, found his nephews and hauled them back.

"Everybody slept on the floor," Carlos says. "One blanket each."

Reunited with his sons, Zenon tried to be a good father, but it wasn't easy. Jose and Carlos acted up in school, jumping from their seats and constantly fighting. Their dad and grandfather punished them.

"It got to the point where they were hitting me before school," Carlos says. "They'd say, 'I'm hitting you because I know you're going to get in trouble again today.' "

His grandfather took him out to the fields for a taste of manual labor. Carlos, still in elementary school, had to carry heavy boxes to a truck where the boss punched his ticket.

This hard lesson did not stick. As Carlos and Jose continued fighting – "We were always so hyper," Jose says – the family tried something different: boxing.

The owner of a local gym took one look at the brothers, who were 7 and 8, and told them to come back in a few years. But they noticed another boy their age working out.

"That's my grandson," Zenon recalls the owner saying. "He's been training for more than a year."

Zenon proposed a deal: If Carlos defeated the grandson in a bout, his kids got to stay. Jose recalls: "My brother beat him up. Made him cry."

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Picnics, birthday parties, barbecues after church – it seemed that wherever the Balderas family gathered, someone broke out the gloves.

"We loved to box," Zenon says. "Even if we were tired from the fields."

They knew it was a dangerous sport, that kids could get hurt in the ring, but Zenon became convinced it would help his sons. That is why he made them train every day. That is why he gave them whuppings when they skipped workouts.

"I told myself I needed to do something," he says. "I didn't want them to be the same as me when I was young."

With no one to give them a ride – and no bus money – the brothers carried those duffel bags a mile each way, looping the strap over one shoulder, then the other and finally across their heads.

The family eventually left the gym over an argument. Zenon wanted the boys fighting every month but the owner thought them too young for so much action. Zenon finagled a key to a gym 30 miles south in Lompoc.

For the next four years, he trained them every night. When the drive grew too wearisome, he and his brother David cobbled together rent for the warehouse, opened their own gym and invited other kids.

"Look around Santa Maria – all you see are strawberry fields and convenience stores," David says. "If you don't go to school, if you keep getting in trouble, you end up working in the fields or one of those stores. Or you end up in a gang."

If Carlos sometimes bristled at training, there was no doubt about his love for the sport. He began carrying around gloves, challenging classmates and neighborhood kids.

"Little by little," he says, "they didn't want to spar with me anymore."

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Home movies show the 7-year-old standing flat-footed in the ring, his oversized shorts making him look puny as he trades shots with an opponent.

"Our styles weren't so good," Carlos says.

Quickness and energy carried him at first, until he began learning the nuances of the game. Soon after becoming eligible for official competition at 8, he won his first tournament – defeating his brother in the final – and started fighting up and down the coast.

"I was nervous," he says. "A lot of people don't ever get to leave Santa Maria."

Money was a challenge – the grandfather once had to hock his watch to put food on the table – but the family found a way to get the brothers to competitions.

Carlos traveled to Alabama for the 2011 Junior Olympic national championships at 15. A gold medal at the PAL championships in Ohio the next year propelled him to bigger victories and a spot on U.S. teams that competed internationally.

"Carlos was one of those kids always in the finals, always fighting tough opponents," says Kay Koroma, a resident coach for USA Boxing. "You knew this kid was going to be somebody."

Videotape of a recent bout against a Moroccan fighter shows him moving effortlessly, changing angles, flicking a jab before ducking to fake a body shot. When the other guy covers low, Carlos comes over the top with a knockout punch.

"I like to make my opponents look clumsy," he says.

Last year, he won four of five bouts on the amateur World Series of Boxing circuit, losing only when he was accidentally head-butted by the top-ranked fighter from Azerbaijan.

Shortly after Thanksgiving, USA Boxing called to inform him that he had accumulated enough points to qualify for Rio, no need to win the trials. His dad cried.

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Was the father too tough on his son?

Carlos shrugs and says boxing kept him in high school so he could earn a diploma. It allowed him to travel the world and – after Rio – figures to make him good money when he turns professional with his brother.

"When I was younger, I'd get in trouble for fighting," he says. "Now I get rewarded for it."

After all these years, the father still has his doubts but answers the question with one thought.

"At the end of the day, Carlos is an Olympian," Zenon says. "So something good came of it."

The day after a sparring session with pro champion Leo Santa Cruz – the family pitched in gas money for the drive to Los Angeles – they keep the workout short.

Strapping a thick pad across his midsection and slipping boxing mitts over each hand, Zenon climbs into the ring. He whispers encouragement as Carlos throws punches, exhaling sharply with each combination.

They move around the ring in unison, from one corner to the next, in a waltz they have done together so often. After about 10 minutes, the son lands one more shot, and the father quietly backs away.