I want to add to the current top answer, to contrast it with a different but similar expression "the ball has been dropped". I'm adding this here because someone else might come across your answer when it is this other expression that they are encountering.
This comes from the metaphor of juggling balls. which means something completely different and is not even vulgar as is even part of acceptable corporate office-speak. It means that something that needed constant attention/maintenance was neglected and it is ruined.
The key to distinguishing between the phrases is "ball" versus "ball s". In the plural it almost always means testicles (and is crude) in the singular it refers to this other phrase. A notable exception being "Having multiple balls in the air" it a counterpart to this expression (ie "the ball has been dropped", in this can meaning that there are multiple things and none of them have been yet "dropped") and not testicles.
Once again, this is a SIMILAR expression but DIFFERENT from the one you have asked about.