'ballock' originates from Old English, specifically the word 'bealluc' (also recorded as 'bealluc[a]'), where the root referred to a 'rounded lump' or 'ball-like swell'.

'bealluc' changed in Middle English to forms such as 'ballok' and 'bollok', and eventually into the modern English forms 'ballock'/'bollock'.

Initially it meant 'a small round object' or specifically a 'testicle'; over time the word retained that anatomical sense and developed figurative senses (e.g. 'to scold', 'to bungle') and, in plural, the emphatic slang sense 'nonsense'.