'ballpark' originates from American English, specifically the compound of 'ball' and 'park', where 'ball' referred to the sport 'baseball' and 'park' meant 'an enclosed area or playing field'.

'ballpark' formed in the late 19th century U.S. as the compound 'ball-park' referring to a baseball ground; it later lost the hyphen and became the modern English word 'ballpark'.

Initially it meant 'a baseball stadium or playing field', but over time it evolved into additional meanings such as 'a rough estimate' and the verb 'to estimate roughly'.