Baseball, from Nintendo's in-house R&D1 studio, is a rudimentary version of the sport of the same name that Nintendo created for the NES and the Game Boy. The game was a launch title for both respective systems in the US, first on the NES in 1985 (the Japanese Famicom version was released in late 1983, a few months after the system's debut) and subsequently on the Game Boy in 1989 (it was also a launch title in Japan).
It is notable for being one of the first Game Boy games to be configured for use with the Game Link Cable, which allowed for multiplayer gameplay between two Game Boy units.
The Game Boy version of "Baseball" was one of the first games available for Nintendo's handheld. It includes Mario and Luigi as captains. Mario himself is featured on the cover.
Mario and Luigi are captains of the team; Mario is the captain of the Bears; Luigi is the captain of the Eagles. The player can select them as their pitcher if they wanted, but graphically all the pitchers look the same. The rest of the team pitchers have common English names, such as "Paul","Randy","Sam", and "Jimmy."
During this era, Nintendo would often include Mario in games just for appearances' sake to help sell the game, though often it wasn't really possible to control Mario in many of these games. Other examples of this is Mario is the ref in Tennis and the paddle in Alleyway.
Nintendo re-released the NES version of baseball for their short lived GBA e-reader attachment. The game came in a pack much like a pack of baseball cards. There were a total of 5 cards that had to be scanned by the e-reader in the correct order. On the back of each card provided screenshots of the game as well as tips and instructions.