When Koo arrived in Ridgewood with his mother as a sixth-grader, he knew nothing about football. Koo did not even speak English. In fact, soccer was the sport he played before coming to the states. So he had no clue about the two pro football teams that shared a stadium just 20 minutes away.

Quickly, Koo was introduced to football at recess by a friend who asked him to play. Koo launched the ball and left soccer in the past. He began his journey as a football player the following year in seventh grade. At Ridgewood High School, Koo was an all-league receiver and cornerback in addition to excelling as a kicker and punter.

He went on to play at Georgia Southern University, where he left his offensive and defensive days behind him. He had one of the greatest years in school history during his senior season, earning third-team all-American honors.

Following his time at Georgia Southern, Koo was signed as an undrafted free agent by the Chargers and made the roster, beating out kicker Josh Lambo. Then, his career took a turn for the worse.

When the Chargers released Koo in 2017, he did not hear from another NFL team for nearly two years. As time went on, Koo questioned himself and his skill.

What am I doing? Koo thought to himself, What am I doing with my life?

"Some days, you're hopeless," Koo recalled.

The experience taught him the difference between motivation and discipline.

Koo was motivated to get back to the NFL and had a plan to work out every day, to improve his mechanics and other techniques. But there were many days where it felt pointless. Days where his motivation wavered — or was not present at all.

"I realized that discipline is what's going to take you to where you want to go," Koo said.

In Jan. 2019, Koo tried out for the Atlanta Legends, a team in the new American Alliance of Football. It was not his ultimate goal, but this opportunity gave him a shot to prove to NFL coaches and scouts that his performance in Los Angeles was an aberration. In eight games with the Legends, he was perfect on all 14 field goal attempts — with current Falcons punter Cameron Nizialek holding his kicks.

NFL coaches took notice. After a brief practice squad stint with the New England Patriots, the Falcons signed Koo in Oct. 2019. In his debut, Koo made all four field goals and both extra points, earning NFC special teams player of the week honors.

"I wanted to be someone better than what I was with the Chargers," Koo said. "Because, if I didn't improve after what I went through, it didn't mean anything. That's kind of the growth mindset that I picked up."

Koo has his hat backward and is on the far practice field at Falcons headquarters in Flowery Branch with other specialists. It is a cool Thursday before the team heads to MetLife Stadium to play the New York Giants – somewhat of a homecoming for Koo.

He isn't kicking in the open practice available to the media. He is on the far field, playing catch with long snapper Josh Harris. In his 10th season in the NFL, Harris has become a role model for Koo. Harris, often just by example, has taught Koo about being a professional, the importance of having a routine, among other skills that have made him a better player.

And the respect goes both ways.

Harris and Koo spent almost every day in the offseason training together. Each time Harris became more mesmerized at how Koo approaches every training session.

"He really brings it each and every day," Harris said, "in the meeting room, in the weight room, and on the field. He's earned everything he's gotten."

And because Koo pushes himself near his limits each time he trains, he likes to do as little as possible when he is not working out. Even in relaxing, he has found a way to improve his craft.

The secret? Golf.

"I like golf because when I go into the gym, I'm busting my ass for two hours and when I'm done, I don't want to do much, and golf's chill you're kind of just hanging out," Koo said with a chuckle. "And there's just so many similarities from kicking to the mental aspect of it to the swing thoughts. A lot of mechanics relate to kicking. And it's fun and competitive."

Koo's aggressive mindset to training is what special teams coach Marquice Williams loves about him. Williams describes Koo as a football player first because of his background at other positions. Williams was a Chargers special teams assistant when Koo was with the team. Now, Williams is amazed at how much Koo has developed in the short time.

"He's really easy going, but he is really serious about his job now," Williams said. "He's really found his groove and his routine. The biggest thing was finding his routine and what works for him. It's great to see where he started and where he's at now."

Over a decade since he left South Korea, Koo still keeps his native land close to his heart. He has a tattoo over the left side of his chest that reads, "Never forget where you came from; it might save you from where you could end up."

Koo is just one of four South Korean-born players to play in the NFL, joining Hines Ward, Kyle Love, and John Lee. Per Statista, the NFL was just 0.1 percent Asian in 2020 and, because of that, Koo understands that each time he steps on the field, Asian American children see what is possible.

"I hope Asian American kids do see me and think, 'Maybe I can be that too,'" Koo said. "Whether it is in football or whatever it is."

Koo generally does not speak publicly about his identity as an Asian American and the marginalization that it comes with. But after a man shot and killed eight people at three different spas in Atlanta last year, including six women of Asian descent, he spoke up on Instagram.

With a picture of the back of his Black Falcons helmet showing the decal he wore last season, "Stop Hate," Koo wrote: "As an Asian American, I have heard the jokes and name-calling. I often dealt with it by ignoring what was said and minding my own business. I don't have all the answers, but I realize now more than ever that this is an issue that needs to be addressed and that ignoring it won't help us do that. I know this one post won't solve the problem, but I hope to help raise awareness on hate crimes against all. #stophate ✊✊🏻✊🏼✊🏽✊🏾✊🏿♥️"

Koo's post was a rare sign of vulnerability on his Instagram page, usually reserved for football pictures. He stepped outside of his comfort zone because of his large platform — he has 160,000 followers on Instagram — and for the people who look up to him for guidance.

"I think at the end of the day, everybody goes through something, and when you can see somebody going through the same thing as you, it helps you," Koo said. "So if I can just reach that one person, I'm definitely gonna try."

Koo's 40-yard game-winner silenced the crowd at MetLife. Koo's family and friends celebrated loudly from their box; Sempier gave a fist bump and smile as Koo celebrated with the team.

"Having him there meant the world man..❤️," Koo wrote on his Instagram Story.

Sempier is known as a kicking guru in New Jersey. He mentors kickers across the state, free of charge. He and Koo met 12 years ago, when Koo was a high school freshman, and have talked almost every day since.

"It was one of the best moments in my life," Sempier said via phone call a day after the Giants game, as he prepared to workout a kicker at Depaul Catholic High School in New Jersey. "He worked so hard to get to where he is."

Kicking is one of the most challenging jobs in the NFL. A position with almost no room for error. A few mistakes and your NFL career could be over — like Koo's almost was with the Chargers.

So Koo never gets comfortable.

Even after a Pro Bowl season, he knows firsthand how quickly things can change in the NFL. He uses the lessons from his time with the Chargers to ensure he never feels like he did for two years, unsure if his pro career would continue.

And If Koo continues to hit game-winning field goals and have seasons like he had last year — forget about just playing for a long time — he could become one of the NFL's next great kickers.