The main mode in Bad News Baseball is the one-player mode. In this mode, the player must defeat every other team featured in the game in any order in a round-robin style. Wins and losses are not recorded, and the player can continue playing indefinitely until all other teams are defeated. While this means there is not a set schedule of games, pitchers do have a stamina rating that once depleted, will take several games' worth of rest to recover from.
On the initial screen, players can choose to play 1 or 2-player games, spectator mode (CPU vs. CPU), a 1 or 2-player All-Star game, or enter a password. Passwords are given out after every game and record what teams the player has beat, as well as the pitcher's stamina levels.
Functionally, the game plays similarly to R.B.I. Baseball, which is another baseball game that was released for the Family Computer in 1986 and the NES in 1988. There are some differences aimed at a younger audience like anthropomorphic rabbit umpires and kid-friendly animations for events such as home runs and close plays. In addition to this, players can become unconscious when they are forced out or knocked out by the ball. Similar in Nippon Professional Baseball (Japan's professional baseball league), the game will end in a tie after 12 innings.