An El'Aurian con man named Martus (Chris Sarandon) visits DS9 and stumbles across a bizarre gambling device that—once replicated and integrated into his newly established casino—inadvertently changes the laws of probability so that unforeseen unlikelihoods occur on the station.
"Rivals" is an atypical attempt at light cleverness, and it almost works. This is a relaxing, diverting hour with enough sense of whimsy to be respectably entertaining. Particularly fun to watch are the humorous character moments surrounding O'Brien and Bashir's racquetball rivalry. Watching O'Brien's frustration over Julian's youth advantage is a delight, and Bashir's own problem of having to beat a person he considers a mentor is a witty twist.
Less compelling are the implications of Martus' competitive establishment stealing all of Quark's customers—though the idea isn't completely unpalatable. Quark's idea of conning O'Brien and Bashir into a "charity" racquetball tournament to regenerate his business is somewhat inspired. And the results of the tournament prove interesting when the change in the probability laws causes the ball to always go to O'Brien—a fairly clever idea.
But there's a glaring flaw surrounding this episode, which is that the writing is far too restrained and low-key for what the premise demands. Menosky should've pushed the envelope on this one so much further into comic mayhem—or at least into mild slapstick or memorable creativity. As it stands, "Rivals" is an amiable, lightweight episode with some good ideas, but just not funny or inspired enough to maintain a real sense of energy.