With that in mind—and taking the Oakland A’s as his inspiration—in 2004, Mike Kerns left his job working for sports agent Jeff Moorad, now general partner of the Arizona Diamondbacks, to accept millions of dollars in Silicon Valley venture capital and open a jock exchange called Protrade. (His co-founder was Jeff Ma, the ringleader of a group of M.I.T. students, made famous by the book Bringing Down the House, who won more than $3 million from Las Vegas casinos.) On the surface, Protrade, which has its headquarters in San Mateo, California, looks like another fantasy-sports website, but just below the surface lies the model for the jock exchange. Like a market in corporate shares, Protrade trades year-round and in real time, and a lot of different people can buy the stock and own, in effect, little pieces of an athlete. They can watch their Peyton Manning stock rise and fall from play to play during the season and see what happens if he’s traded to another team in the off-season. The exchange also allows them to short the jock’s stock—to profit from his poor performance. Each stock pays dividends, which gain in value based on the athlete’s on-field performance.

Protrade’s goal is to model the underlying reality of a sport. It’s the reason the company employs researchers, and it’s what got Protrade hired to consult for the Portland Trail Blazers and San Francisco 49ers. In the beginning, this market will probably be based on cruder and more widely understood performance stats. “But,” says Kerns, “as the market grows and the liquidity and sophistication of institutional investors increase, there will be trading products that require more-sophisticated analysis, and we’ll need to truly quantify the value of an assist that leads to a dunk versus an assist that leads to a 5-foot jumper, or the value a running back should receive for a 3-yard run versus an 8-yard run, compared with the value received by the offensive line.”

In 2005, the Tampa Bay Buccaneers’ rookie running back, Cadillac Williams, became a star by racking up nearly 1,200 yards, averaging 4.1 yards per carry. One year later, Williams ran for 798 yards, with only 3.5 yards a carry, becoming, apparently, mediocre. But the sophisticated investor might attribute Williams’ trouble to Tampa Bay’s play calling, which was usurped by the head coach, Jon Gruden. Indeed, the stock in Williams would eventually comprise information about the value of his offensive coordinator, offensive line, fullback, and everything else that alters, however slightly, Williams’ ability to run. Williams won’t need to complain to the press that he’s being misused. His shares will complain on his behalf.

A jock stock’s price is driven not directly by the athlete’s performance, but indirectly by supply and demand for the stock (just as in the real stock market). An athlete’s performance is important, of course. It’s the equivalent of corporate earnings. But the price of the stock is set by the market. A bet on the future dollar value of a player isn’t really based on the player’s performance, but on the market’s perception of that performance. The successful investor will need to predict who will play well and how play in general is understood. As it happens, we are living through a period in which the interpretation of athletic performance changes rapidly. For example, Houston Rockets forward Shane Battier doesn’t score a lot of points or snag many rebounds, and as a result, he isn’t considered a terribly interesting basketball asset. But when Morey became assistant G.M. of the Rockets in 2006, he was less interested in Battier’s points and rebounds than in the effect Battier’s presence on the court would have on his team’s points and rebounds. (It greatly improved both.) The Rockets obtained Battier in a trade before the 2006-2007 season, and his perceived value rose.

Here is the most intriguing possibility of this new market: It will create a feedback loop between itself and the salaries of pro athletes. Say, for example, a team of M.I.T. mathematicians managing a hedge fund based in Greenwich, Connecticut, has proven that running backs are far less important to a team’s rushing yards than right guards are and, therefore, that the N.F.L. is underpricing right guards and overpricing running backs. The fund is set to make a lot of money in guards and running backs, but merely having a stunning insight or creating a new piece of sports knowledge won’t be enough. The smart thing for the hypothetical hedge fund to do is to buy up a portfolio of star right guards, short a portfolio of running backs, and then release its information to N.F.L. teams so that they will start paying more for right guards and paying less for running backs.