Ballparks became sources of profit for individual vendors, concessionaires, and surrounding neighborhoods. Card collecting evolved from hobby to investment. And as television and advertising transformed society, they also transformed baseball, gradually reshaping relationships between players and products, between fans and the game.

Professional baseball. The familiar phrase illustrates that what began as recreation quickly became an industry. By the mid-19th century, teams already were evolving from amateur clubs into moneymaking ventures, nourished by the Industrial Revolution in which growing cities and rising incomes created new audiences. Baseball quickly divided between "labor" and "management." Players seeking higher salaries and control over their careers organized—the roots of today's Players' Association. National and American League owners established governing institutions (first a three-person Commission, later a single Commissioner) to make and enforce rules on and off the field and preside over the sometimes hesitant expansion into new markets.

"Good fences make good neighbors," wrote poet Robert Frost. Good fences also make good business. An enclosed ballpark can charge admission.

The first gate charge, in 1858, raised funds for charity. It also showed there was money to be made, demonstrating the public's willingness to pay for play. By the late 1860s, ballparks regularly sold tickets.

Today, ballparks are business ventures. Ballclubs generate profits from tickets, advertising, even selling the stadium's name. They create income for owners and concessionaires. Promotional gimmicks, from clowning on the field to "bobblehead" doll giveaways increase attendance and sales, while luxury boxes bring high-paying corporate clients.

Candy bars. Aftershave. Underwear. What's their connection to baseball? Advertising. Eager to capitalize on the game's popularity, merchants and manufacturers link products to the national pastime.

As mass production flooded America with consumer goods in the late 19th century, merchants searched for ways to draw customers. Baseball themes and player endorsements flourished. In 1920, Babe Ruth earned more from a single endorsement than any teammate earned for a year of play.

Today, businesses treasure links to baseball. For instance, in 2001 a major credit card company signed an $81 million, five-year agreement with Major League Baseball, its biggest domestic sponsorship. Marketing messages fill every stadium, and teams depend on income from advertising, be it on the air, on the field, or on its merchandise.