Green’s Dictionary of Slang

(US) a stupid or silly person; used in response to an unintelligent action, as a sarcastic response to a foolish remark or as an observation on someone’s character (or lack thereof).

1997–2002

Alt. Eng. Dict. 🌐 ball (noun) stupid or silly person Generally used in response to an unintelligent action, such as in ‘Don’t be a ball’ or sarcastically responding to something stupid said: ‘Okay.... ball’ or as an observation of another’s character ‘Hope is such a ball.’ This word comes from the reference to the testicle.