I just want to remind you to the only one rule at the moment:
Please use a balanced roster, i.e. positioning true to position. Avoid known glitches like only 1-play-defense. Try to keep the game as realistic as possible.
This means that you have a balanced roster and should use every player on their actual position. There should be no weight advantage for some players in a different position.
When you have a player listed as a FB, to have him underweight, while playing him exclusively as TE #1 - it's against league rules. It's even underscored..
Not having any player at a certain position, at all, is the same thing..
