I selected a RB that is going to play RG, but when I put him in his position they tell me that he is 28% underweight. Will that settle over time? or that player will never be suitable for that position?
It depends on the player. Players have a hidden frame trait. While not 100% accurate the best indicator of how much they can gain or lose depends on their starting (draft) weight at their natural position. So for example a 225 lb RB can gain more than a 215 lb RB. I'm just guestimating but to reach full ol weight a RB would have to start at 230+ lbs. Otherwise he'll be underweight his whole career and his starting weight will determine by how much.