partisan
PAR-tih-zunadjMeaning strongly supporting one side, often without fairness
Memory hook PART-isan: on ONE PART (side) only. Grandpa wears his team’s colors from hat to socks, cheers every play for his side and boos every call against it; he is partisan.
The partisan crowd booed every call that went against the home team.
In context A fair referee must never be partisan; if she favors one team, the whole game becomes meaningless.
Similar one-sided, biased, prejudiced, factional
Opposite impartial, neutral, nonpartisan
From French partisan, from Italian partigiano, from parte (part, side).