Roto Grip Inc. has taken advantage of a quirk in the rules which dates back to the early '70s to fashion its newest ad campaign. It is ballyhooing its new SD-73 as a ball that was "banned from the PBA Tour," and "The first 'true' cheater ball." After fielding several questions, like "What's that all about?" and, "Has it really been banned from the Tour?" we decided an answer was necessary. And it's this: The PBA has a 75 hardness rule, created as a cap in the wake of all the super-soft "soakers" which were used on Tour back in 1973, while the ABC reacted to the same phenomenon in coming up with its own rule, capping the hardness at 73 on the durometer scale. The SD-73, as its name implies, passes ABC's hardness rule, but not PBA's.