Negative Points Details Done 
If you set this option to no, your players will never lose fantasy points for having a negative yardage total. So, a player rushing for 0 yards would receive the same points as a player finishing the game with -10 rushing yards.

By choosing to allow negative yardage points, all players receive negative points for every yard lost. So if your league awards one point for every 10 rushing yards, you would lose one fantasy point for every 10 yards lost.

If you wish to award negative points for a specific scoring category, simply enter a negative number as the point modifier for that category.

Done