A different ball game
Meaning
A completely different situation or set of rules.
Usage
Used when comparing two contexts that are not directly comparable.
Origin & History
Origins and dates here are approximate summaries. Many idioms have disputed or unknown origins, and not every date has been checked against a historical dictionary, so treat specific dates and stories as a starting point rather than a citation.
Sports metaphor for contests that use different rules or equipment.
Seen in American newspapers by the early twentieth century, especially in sports commentary.