Pro Yakyuu World Stadium '91 is a baseball game for the PC Engine and the second and last World Stadium game for the console, which spun off Namco's Family Stadium (or Famista) series. "Family" was a common word used in the titles of NES games due to the system's Japanese name of "Family Computer", so Namco dropped it for their non-Nintendo baseball games and used "World Stadium" instead. Subsequent World Stadium games were released for the Arcade and Sony PlayStation.
As with the Famista games and its World Stadium predecessor, the game depicts its baseball players as super deformed characters and focuses on Arcade-style gameplay rather than a serious simulation of the sport. The player can still customize teams before games, and there are options for up to four human players to compete. The player can also choose to watch two CPU opponents challenge each other.