Of all the ``isms,'' implies this gossipy and savvy rundown on big-time tennis, commercialism may be the most subtly ruinous. Hitherto known as one of college basketball's better Boswells, Feinstein (A Season on the Brink, A Season Inside, Forever's Team) spent 1990 with the young professionals who make often-handsome livings on courts of quite another kind. By his account, few of the men and women on the global circuit (let alone their agents or tournament officials) can be described as sportive. With millions of dollars in prize money and endorsements for corporate sponsors at stake, touring pros and their supporting casts play the game for keeps. The long grind of the season starts in January with the Australian Open, the first of the so-called Grand Slam tournaments on which the author focuses, and ends in December with the Davis Cup final. In between, there are nearly 80 more sanctioned events for men and over 60 for women, plus countless opportunities to participate in lucrative exhibitions. As it happened, 1990 produced eight different Grand Slam champions and some very fine tennis. In covering the major contests, though, Feinstein leaves little doubt that the administrative policies of the game are as anarchic and self-seeking as those of boxing, a situation that helps explain the willful, mercenary bent of many star attractions. The author does not confine himself to muckraking, however. Indeed, he has kind (if blunt) words for such top seeds as Boris Becker, Chris Evert, Ivan Lendl, John McEnroe, and a host of lesser lights who have some appreciation of the cosmopolitan sport's traditions. Feinstein is obviously disturbed, though, by the increasing incidence of ``tanking'' (deliberately losing a match), TV dominance, conflicts of interest, and parental ultimatums. He's also bemused by the game's expedient approach to finance. For example, Zina Garrison (a talented black woman) couldn't buy an endorsement until she made the 1990 Wimbledon final, at which point her agent negotiated a $500,000, five-year deal with Reebok. An unsparing but engrossing audit of a sport that has yet to reckon the price of winning at any cost.