The champions will be chosen by an impartial selector:
I will personally be ensuring that no underage student hoodwinks our impartial judge into making them Hog-warts champion.
An impartial judge will decide which students are most worthy to compete for the Triwizard Cup, the glory of their school, and a thousand Galleons personal prize money.
"Who’s this impartial judge who’s going to decide who the champions are?" said Harry.
"S’pose not…… " Harry rolled over in bed, a series of dazzling new pictures forming in his mind’s eye…… He had hoodwinked the impartial judge into believing he was seventeen…. he had become Hogwarts champion…. he was standing on the grounds, his arms raised in triumph in front of the whole school, all of whom were applauding and screaming…. he had just won the Triwizard Tournament.
There are no more uses of "impartial" in the book.
Show samples from other sources
An impartial judge is necessary for a fair trial.
Some studies require the impartial eye of a scientist.