so it would have to overturn the ruling on the field of a first down or touch down right? meaning you couldn't just challenge that the ball was 1 yard further ahead?
I'm not sure.
I just think I've seen it before where say the ball was marked in the middle of the field say 1 yard short of a first down, and the Coach has challenged the play of an incorrect spot on the field, and the referees have overturned the ruling on the field, thus saying that the ball was 2 feet further or something, thus still being short of the 1st down by 1 foot. Thus, the Coach successfully challenged a play.