This was uttered in an interview. It is a mash up of “wait for the other shoe to drop” (wait for the next seemingly unavoidable thing to happen” and “drop the ball” (make a mistake). The speaker may have been thinking of the New Year’s Eve ball in Times Square, and waiting for it to drop to usher in the new year. Or perhaps the Road Runner cartoon where the anvil eventually drop on his head. “Drop” is the culprit here, appearing in both idioms. This malaphor seems very appropriate these days in the U.S. A big thanks to Sam Edelmann who heard this one and dropped it on me.