Negative points applies to yardage categories only. If a league awards 1 point for every 10 rushing yards and the commissioner selects "No" for negative points, a player who rushes for negative 10 yards receives 0 points (not -1).
If the commissioner of your league selected a negative point modifier for a scoring category (such as -2 points for interceptions), then a negative score can be earned by a player in a given week. This occurs even if the commissioner selected "No" for negative points.
Similarly, if the commissioner selected a fractional point modifier for a scoring category (such as .25 points per rushing yard), then scores earned by a player might be represented in fractions. This occurs even if the commissioner selected "No" for fractional points.