on the bubble

Meanings

1. Holding the last qualifying position with qualification still in progress, and thus liable to lose that position.
2. Having qualification for an event depend on the upcoming performances of other competitors; hence, at risk of being eliminated, and reversely, being close to qualification; on the verge.
3. Uncertain of success.
4. Used other than figuratively or idiomatically: see on, bubble.

Etymology

First appears in the US, c. the late 20th century, from the state of Indiana motor racing.