Some fabrics say on the selvage for personal use only and not for commercail manufacture. If that is the case then I would say you definately can't sell anything you make with those fabircs even if it is your own design.
The second question is the actual project . People who release patterns for sale or for free will state ( or should) what the limitations of your use are. this can be for personal use only. A limited number of items allowed for sale without asking further permission. Limited permission for chairty sales.
What most people are interested in is credit for the design, but if there isn't any information on the pattern you should always contact the person and ask.
The case of the NFL fabric is interesting. Does it say on the selvage not for commercail manufacture? I know the official flower fairies stuff does.
Becks