Is it ensure, insure, or assure?
1812, frequentative of bob (v.1). The notion is "to move or handle something with continual bobbing." Related: Bobbled; bobbling. Bobble-head as a type of doll is from 1968.
: The President's denial was a bad bobble
To blunder; esp in baseball, to mishandle or drop the ball (1900+)