R.B.I. Baseball was originally released in Japan under the name Pro Yakyuu Family Stadium on December 10, 1986, as part of the Family Stadium franchise. The US version, a port by Atari Games (under the Tengen label) released on January 5, 1988, features a license from the Major League Baseball Players' Association, allowing it to have real baseball players on the roster. However, due to a lack of the core MLB license, the game doesn't contain real teams, referring to all of them by city name only.
Despite having actual MLB players' names (although sometimes truncated), each character looked exactly the same (e.g., there weren't any black players, everyone was the same height, etc.). The only visual differences among the players was whether they were right- or left-handed, and if pitchers threw overhand or submarine-style. Performance characteristics among the players were present however, with batting average, power, and even running speed distinctions between individual players being reflected in the game.
After this point, the Namco-developed Family Stadium series and the Tengen-shepherded RBI Baseball line would diverge, with Tengen producing two more games based on this core before moving to 16-bit machines and an all-new, domestically-developed game.