From October to June, Iñaki OSA Goikoetxea—Goiko to his friends and admirers—plays professional jai alai six days a week at a fronton behind the Miami International Airport. Built in 1926 and simply called Miami Jai-Alai, the ungainly sand-colored facility looks like a South Florida riff on one of Saddam Hussein's concrete palaces. When it opens at noon, the spectators, most of whom appear to be eligible for Social Security, begin arriving for the daily matinee performance. They hobble across the lobby's liver-spotted tile to the betting windows, where they place wagers on the action in the cancha, the caged playing court. Some never make it into the arena, instead slumping on black vinyl stools and watching the matches on closed-circuit TV like gamblers at an off-track-betting parlor. "Miami Jai-Alai is known as the Yankee Stadium of our sport," Goiko says. Then he pauses, considering what that reveals about the state of the game today. "Please, do not say anything bad about Miami Jai-Alai," he adds.

Goiko is 31 years old, six feet three, and 220 pounds, with dark, serious eyes and thick black hair that dips over his brow in a Superman curl. Like the sport he plays, he is Basque. He grew up in Zumaia, a humble fishing town about 20 miles west of San Sebastián. Since going pro, he's won nine world titles—five in singles, four in doubles—at the tournaments hosted in Europe by the International Federation of Basque Pelota, the closest thing jai alai has to a governing body. By common assent, he is considered the best player in the history of the sport. "It's even better than having LeBron," says Juan Ramón Arrasatte, the players' manager at Miami Jai-Alai and Goiko's boss. "With LeBron, you can talk about Kobe or others. In this sport, nobody else comes close."

"Jordan doesn't have nine titles," Goiko observes, sounding more stoic than boastful. "Kobe doesn't have nine. LeBron has none. Kelly Slater has eleven, so I have to catch up to him." He knows perfectly well that his sport is a speck compared with the NBA or even pro surfing. "I play jai alai," he acknowledges. "I am not exactly famous." Miami Jai-Alai pays him an annual salary in the five-figure range. He has no endorsement deals, no agent, no entourage, no groupies. He does have the single-word nickname befitting a champ and his own bobblehead doll, which he proudly presents to me as a gift. And despite his obscurity, he has the drive of a superstar athlete. "I'm always looking to find the monster in me," he says. "I win by finding the monster."

Cesta Punta World Championship opener.

Goiko was 7 the first time he picked up a cesta—the oblong basket of steam-bent chestnut wood and woven Pyrenees reeds that jai alai players use to fling the goatskin-and-latex pelota at up to 180 miles per hour (boosters call it the fastest sport in the world). "Jai alai wasn't even that popular in my town," Goiko says. "I played because my brothers played. I wanted to be a professional surfer." But he also wanted to get out of school and didn't want to work on his father's fishing boat, so when a scout from a now-defunct fronton in Milan offered him a contract at 16, he moved to Italy. Word of his talent spread, and in 1997 he was invited to play in Newport, Rhode Island. From 1998 to 2002 he played in Orlando, then took his talents to Miami.

At its peak in the 1970s, Miami Jai-Alai frequently drew crowds in excess of 10,000. But on this gorgeous, 80-degree Thursday afternoon in late January, 16 athletes compete in front of 15 spectators. The upper tiers of the arena aren't even accessible. Down below, the onlookers sit dotted along the 176-foot-long cancha. "Last call, place your bets," intones a voice over the PA system, followed by an electronic countdown of slow, irregular bleeps that make it sound as if the whole place is hooked up to a heart-rate monitor. The players wear numbered jerseys, heavy helmets, and white pants with red sashes. Using their cestas, they produce powerful, caroming shots that have blown out knees and dislodged eyeballs. (In a 1986 episode of Miami Vice, one even killed a man.) They dive to the floor and crash into walls trying to keep balls from bouncing twice or leaving the court, which would result in losing the point. Through the screen that protects the crowd, they look like video-game characters—high-def agglomerations of pixels that jump, lunge, and sling sine waves at the granite front wall.

But the spectators don't cheer for the heroics on the court. They cheer for their wagers, which fall under almost every betting scheme imaginable—daily doubles, quinella boxes, exacta perfectas. "Let's get this shit together," one woman shouts at Goiko as she paces the barren aisles. "I've been here for 40 fucking years. Get his ass out! Work it, baby!" The crowd's indifference to the players' efforts can make jai alai seem like the loneliest sport in the world.

Because his serving shoulder is bothering him and he wants to be ready for the Citrus Invitational, a major tournament in Orlando this weekend, Goiko plays conservatively and wins only one of five matches. "In Spain and France," he remarks afterward, "they treat you like a professional." He still plays the sport in the Basque region and Biarritz from July to October. There he can earn as much as $15,000 a month playing in front of fans who pay up to 50 euros for tickets to epic matches that end at 35 points. In Miami, where admission is free, the matches end at seven or nine points and are played in a round-robin format designed to maximize betting opportunities: Eight entrants (either singles players or doubles teams) compete, with two facing off at a time and trying to score a point that will let them stay on the cancha to face the next seed. "Here, it's hardly a sport," Goiko complains, "and they treat you like you are nothing."