Linesperson

The linesperson yelled "Out!", but the chair umpire announced immediately, "Correction, the ball was good."

Tennis player Andrey Rublev was disqualified in the semifinal of Dubai for insulting a linesperson to their face.

If it's nine-all in the fifth set, you got to use it and there's a terrible call because the linesperson was sleeping and the umpire was drinking coffee, of course then it's good you have it.