the.com/partisan

Someone who picked a team before checking what the game even was.

means A person who strongly and often unquestioningly supports one party, cause, or side, especially in politics.

from Comes from Italian 'partigiano,' meaning a member of a faction or party, itself rooted in 'parte' (part, side) — the same root English 'party' and 'part' spring from. It entered French and then English in the 1500s meaning a committed adherent of a faction. The word took on a sharper, militarized edge in the 20th century, when 'partisan' came to mean guerrilla fighters resisting occupying armies — ordinary people who'd picked a side and armed themselves for it, which only deepened the word's sense of fierce, unshakeable loyalty.

origin
from italian partigiano, a guerrilla fighter
also means
a long-handled spear, oddly fitting
modern twist
loyalty now outranks the actual argument
tell
facts change, their conclusion never does
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