The game did not use real life teams from either American or Japanese baseball, instead using 12 fictional teams with all fictional players.

In addition to these 12 teams, players can also create two custom teams, the players of which can have their names and ratings edited any number of times.

For the most part, the game adhered to realistic rules of baseball, though omitting some of the more complex strategies such as the double switch.Like many baseball games from the era in which it was developed, Extra Innings's controls were somewhat primitive.

For example, unlike modern baseball games, rather than the player choosing one player to move independently, moving the D-Pad will move all players in the field in unison.Like most baseball video and computer games, either one or two players can join in for some simultaneous action.