Los Llanitos, Mexico
In a remote corner of northwestern Mexico, six men in leather loincloths volley a heavy rubber ball across a dirt court, using only their hips. They dive and leap like overly muscled ballerinas, struggling to keep the eight-pound projectile from flying out of bounds -- or rupturing their spleens.

This is how extreme sport probably looked in 1500 BC.

With each bone-numbing thwack, the players are reviving the ancient game of ulama de cadera, or hip ulama. The sport was once as popular throughout Mesoamerica as soccer is today, only with higher stakes. The members of one team were typically decapitated after the game in a ritual blood bath intended to appease the gods. (Whether it was the winners or losers who were sacrificed is the subject of continuing scholarly debate.)

Fortunately for the men of Los Llanitos, a hamlet of tough-talking cattle ranchers in northern Sinaloa state, ulama (pronounced ooh-LAH-ma) has undergone a few changes in the millennia since it emerged around the time of the Olmecs. The game later became central to the cultures of Maya and Aztecs, for whom it was both a religious rite and a means of settling conflicts between warring tribes.

"Today, instead of cutting off your head, the loser buys the beers," says Manuel Aguilar, a Mexican assistant professor of art history at California State University at Los Angeles, who is studying the modern vestiges of the game. Starting last year, he and an archaeologist colleague, James E. Brady, began leading graduate students to Sinaloa to do research on previously unexplored aspects of ulama, such as the role of female players and the religious significance of the game's rules.

The project is motivated by both scholarly interest and a sense of urgency. The sport, which is played like volleyball but without a net and using the hips instead of the hands, has been in decline since the 16th century. Spanish missionaries, who disapproved of ulama's pagan roots and ritual sacrifice, outlawed it in most parts of Mesoamerica. But Indians in northwestern Mexico, an area that was largely outside the colonizers' control, continued to play the sport in secret.

Mr. Aguilar estimates that the game was still being played by hundreds of people in Sinaloa and in neighboring Nayarit state as recently as the 1940s. But by the 1970s the number of players had dwindled to a few dozen, in part because of the growing popularity of imported American games like baseball and basketball. Now ulama survives in only a handful of rural villages near the west-coast city of Mazatlán, with an estimated 50 active players.

"In Mexico, people don't know what ulama is," says Mr. Aguilar, 43. "You say the word ulama and people ask, 'What do you eat that with?'" He can barely contain his excitement as one of the players executes a perfect hip volley while pirouetting through the air. The professor keeps a wary eye on the ball as he scribbles a running report on the action.

Seconds later, the ball hurtles out of play, bouncing dangerously close to where one of Mr. Aguilar's students is kneeling with his camera. "If you take your eye off the ball for a second, you're toast," says Luis Ramírez, 39, an art-history student who is working with Mr. Aguilar to decipher the game's complicated rules and symbolism.

The court, known as the taste (pronounced TAH-stay), extends over a narrow rectangle 156 feet by 10 feet. Players, whose numbers vary from three to five per side, win points either by knocking the ball across the end line or when the other team fails to return the ball across the midway line. But points can also be lost on a bad play. The first team to reach eight points wins.

"It's a game of drama," Mr. Aguilar says. "There are no ties. The values have to do with establishing a cosmic order. It's not the pragmatic rules of today's games." He explains that the Aztecs and Maya viewed ulama as a metaphor for the epic battle between life and death, symbolism that became reality with the sacrifice of the members of one team.

Curiously, few contemporary players have any ancestral ties to the game. Most are the fair-skinned descendants of Spanish ranchers and typically have little knowledge of ulama's indigenous history or symbolism. But Mr. Aguilar insists that many of the rituals have survived in a kind of collective consciousness. The players are not aware of it, he says. "If you ask them if the game is religious, they'll say 'no,'" he says. "But it's there." He points to a pair of carved stones that the players pilfered from a nearby pre-Columbian ruin to mark the midway point of the court. One of the stones is in the shape of a phallus, an apparent reference to the sport's history as a testing ground for male warriors.

But ulama may not be the men's club scholars once thought. María Ramos, one of Mr. Aguilar's students, began researching the role of women in the sport after finding pre-Columbian figurines of players with breasts. "We were so surprised, because none of the chronicles written by Spanish colonizers mentions women," says Ms. Ramos, 38, who was even more astonished to find women playing in several villages.

Besides the popularity of American ballgames, another factor threatening the game's survival is the scarcity of natural rubber, which gives the ball its regulation weight and bounce. The closest rubber trees are several hours' drive away, in mountains bordering Durango state, where communal landowners charge $300 for enough rubber to make one ball. The total cost, with labor included, comes to $1,000 per ball. Even more daunting is the fact that the rubber trees are in an area controlled by drug traffickers.

"I don't think the game will survive," says Eduardo Páez, a lanky 28-year-old rancher with deep blue eyes who is one of the stars of the Los Llanitos team. "If we lose this, a culture is lost."

Mr. Aguilar is more optimistic. He has been working with the Mazatlán Historical Society to create a ball out of synthetic rubber. The group is also providing free lodging for Mr. Aguilar's research team, which failed to get a grant from Cal State. (The students, most of whom are Hispanic immigrants, were so excited by the project that they paid their own way.)

After a two-hour trip along roads lined with maguey cacti and cornfields, Mr. Aguilar steers his packed minivan into Escuinapa, a bustling commercial town 30 miles south of Mazatlán. Within minutes he locates the town's mayor, who offers to lead him to the cluster of metal shacks that is home to Modesto Guaira. At 68, Mr. Guaira is probably ulama's oldest active player. He is also one of the poorest. When the scholars arrive, he is squatting barefoot in the dirt outside his one-room shack, weaving the straw back of a rustic wooden rocking chair. He'll be lucky if he gets $50 for his month's work.

The furniture maker's haggard face lights up when Mr. Aguilar explains that he has come to talk about ulama. "It's in our blood," says Mr. Guaira, who fields a team with three of his sons and a nephew. He recently began teaching his grandchildren, including several girls. "I told them, it's only for men, but they don't listen," he says, feigning disapproval as three of his granddaughters emerge from another metal shack dressed to play.

The graduate students persuade the kids, some as young as 5, to show off their skills on a patch of dirt strung with drying laundry. The children are fearless, dropping onto the gravely earth to strike the ball from below, in a move known as por abajo. The older children also volley in the air, or por arriba, beaming like sports stars before the flash of cameras.

It is not the first time they have played for a crowd. The family recently began playing exhibition matches at tourist sites more than a thousand miles away in the Yucatán peninsula. The players can each earn up to $600 a month, a fortune for rural farmworkers.

But Mr. Aguilar is concerned that the tourism operators who arrange the games exploit the players -- who generally have little education -- by paying them a fraction of the ticket sales and housing them in tiny, airless rooms. He also worries that the game's traditions are being lost as players focus on making money.

Mr. Ramírez, the art-history student, disagrees. "Kids here, like kids anywhere, play the game because they want to get to the big leagues," he says, as two of Mr. Guaira's grandsons, barefoot and caked in dust, mug for the camera. "Even in the pre-Columbian times, they played for bets. The only thing that is changing is where the money comes from."