CHULA VISTA, Calif. — Something aches deep within Nate Ebner’s chest.

Jogging onto a field at the Olympic training center, he begins warming up with a teammate, the two of them stretching, whipping a ball back and forth.

“I literally feel like my lungs are sore,” he says.

The NFL veteran is accustomed to training camp aches and pains, the agony that accompanies preparing for another season with the New England Patriots.

This is different. This is rugby.

The action doesn’t come in six-second bursts – there is continuous running, passing, tackling and sprinting around the field.

“The feeling of fatigue you get from this game is unbelievable,” he said. “You work yourself to exhaustion and think, man, it’s never going to get any easier.”

Ebner generated national headlines this spring when he took leave from the Patriots to chase his dream of playing for the U.S. team as rugby makes its return at the 2016 Summer Olympics.

Now comes the hard part – winning a spot on the 12-man roster.

“I just keep my head down and keep going,” he says. “Just want to earn respect through my work ethic.”

It is a moment that – in some ways – the 27-year-old has been building toward since childhood.

Rugby was the game his father played, something they could share. Jeff Ebner took his young son along to men’s club practices in Ohio and later coached Nate’s high school team.

At 17, Ebner attended a U.S. developmental camp and became the youngest member of the national program. Playing on the U-19 and U-20 squads, he would eventually be named the teams’ most valuable player at the 2007 and ’08 Junior World Championships.

“Nate was a skilled, tough leader,” said Alex Magleby, performance director for the national program.

But success on the junior level – followed by All-American seasons with Ohio State’s club team – weren’t enough. Ebner wanted something more high-profile.

Switching to football was a tough decision that got even tougher with the sudden death of his father. Jeff was murdered in the fall of 2008 while trying to fend off a robber at the family’s auto reclamation yard.

If grief paralyzed Ebner for a short time, it ultimately fueled his determination. He earned a spot on the Buckeyes’ football team as a walk-on and soon became a standout on kickoffs and punts.

By his senior year, the team had awarded him a scholarship and voted him most inspirational player.

The Patriots saw something in the 6-foot, 220-pound specialist, selecting him in the sixth round of the 2012 NFL draft. Still, it would be a mistake to say that Ebner had left rugby behind.

Each spring, he stayed in contact with USA Rugby officials and continued training with a high-performance team back home in Ohio.

Last season with the Patriots _ in addition to recording 13 tackles and throwing the key block on an 82-yard punt return – he was called upon to try a rugby-style onside kick against the Philadelphia Eagles.

“Rugby was always on my mind,” he said.

Though Ebner toyed with playing for the U.S., the idea did not seem realistic until he read an article in the rugby press that speculated on how he might fit tryouts – and potentially the Games – into his NFL summer schedule.

I actually could do this, he thought.

The Patriots had just signed him to a two-year contract extension, so Coach Bill Belichick and front-office executives would have to give their approval. “I expect him to be ready for the football season like he always is,” Belichick said in a statement.

Veteran players on the U.S. roster – guys who had been toiling for years in anonymity – weren’t surprised when a new face showed up at their training site.

As rugby player Zack Test put it, “We knew people would want a shot at the Olympics.”

It there was any quiet resentment, Ebner wasn’t worried.

“It’s not something I can control,” he said. “I’m here, so tough, you like it or you don’t.”