In August 2002, Ta'u Pupu'a was at a semipro training camp in upstate New York, trying for a second chance at the NFL. Drafted by the Cleveland Browns in 1995, the 6-foot-5, 290-pound Pupu'a, a native of the Polynesian islands of Tonga, had been a defensive end for the Baltimore Ravens until a shattered right arch derailed his budding career. Now, fully healed, he was making a strong showing at practice and feeling optimistic about a comeback.

Still, at the end of every day, there was a nagging voice in Pupu'a's head telling him to do something crazy: move to New York City and become a singer. Finally, one morning he listened. "I didn't even call the coach," Pupu'a says. "I just packed my bags, went to the train station, and headed to Manhattan."

Eleven years later, Pupu'a, 41, has made the unlikeliest of transitions – from elite football player to professional opera star, a Juilliard alum who's performed across the country and in Europe. But the two worlds, he says, aren't as different as they seem.

"Being a singer is like being an athlete," says Pupu'a, who has a featured role with the Danish National Orchestra this month. "You have to be strong, physically and mentally – checking your nerves, singing in front of thousands of people, projecting without a microphone over an orchestra. The lights go on, and it's like walking out onto a football field. When you hit the high C and get the cheer, it's like sacking a quarterback – when I'd look up and see them doing a replay for 80,000 people."

Growing up in Salt Lake City, where his family immigrated when he was five, the soft-spoken Pupu'a had been a tenor in his high school choir. ("I did it on the down low," he says. "I was worried what my teammates would think.") In church on Sundays, people would turn around during hymns to see who was singing.

Pupu'a believed a career in football would be the best way to earn enough money to help his parents and eight older siblings. But through college at nearby Weber State, where he went on a football scholarship, and beyond, Pupu'a never gave up singing. While rehabbing his injured foot, he joined the Utah Opera Chorus.

Despite his amateur experience, when Pupu'a got to Manhattan, he had no idea how to break into opera. He got a job at a restaurant across the street from the Metropolitan Opera House. "In would come Placido Domingo, Marilyn Horne," Pupu'a says. "I'd watch the way they stood, the way they spoke. I wanted to know everything."

In spring 2007, Pupu'a caught a break when he attended an autograph session for opera star and fellow Polynesian Kiri Te Kanawa. He told her he was an aspiring tenor, and she decided to help him. Te Kanawa set up an audition for Pupu'a at Juilliard. He won a full scholarship and graduated three years later.

"Ta'u has an unusually large and impressive voice," says Brian Zeger, artistic director of Juilliard's Vocal Arts Department. "There aren't that many tenors who are able to sing these really big roles of Verdi and Puccini, who can carry over a full orchestra in a house as big as the Met. It's even rarer that it comes in this kind of package: a tall, handsome, charismatic guy."

Looking back, Pupu'a cites desire and persistence as the keys to his success. "When I first got to New York, I thought, 'What am I going to do?'" says the singer, who still lives in Manhattan. "But growing up poor and making it to the NFL, that taught me what this world has to offer. I really had a passion for music. I knocked on many doors, and many were shut, but I just kept going."

Rick Lyle, who played with Pupu'a on the Browns and the Ravens and is now a coach with the San Diego Chargers, isn't surprised by that tenacity. "He was a self-motivator, always pushing harder for every play," Lyle says.

Back then, Pupu'a didn't tell teammates about his love of opera. But today he's proud of his decision to change careers. "Being a man," Pupu'a says, "is all about how you define yourself."