A phenomenon that sometimes happens in pinball games.

Usually multiball is a mode in which high-scoring shots are available, but in a challenging situation since they only remain lit as long as you keep at least two balls in play.

Sometimes you can play an effective one-ball multiball if you manage to get a ball stuck somewhere, such as in the plunger lane, or just hung up somewhere (possibly someplace the ball is normally not supposed to go), or even held on a flipper, though this last requires you use only the other flipper to shoot the other ball. Pinball wizards learn how to pass a held ball from one flipper to the other, which is particularly useful in this situation. However you get it, this can be a lucrative situation because you can shoot at the valuable jackpots while effectively in single-ball play.

Many modern games have automatic plungers and will fire them if a ball falls in the plunger lane during multiball. But you can still try to use the other methods above to play one-ball multiball.

The other way one-ball multiball occurs is when one or more of the switches the game uses to detect when balls leave play are broken. If the game can't tell the difference between one ball in play and two balls in play, then very likely all of your multiballs will last until the end of the ball, including a period of one-ball multiball. You can't really do much about this, though, and it sometimes interferes with other parts of the gameplay.