Rules4

Team rosters are initially stocked during the First Draft, thereafter the roster may be modified through either Supplemental Drafts or through trades with other team owners. No NFL players are retained from one season to the next. All rosters are empty prior to the First Draft. All roster spots must be filled during the First Draft. After the First Draft, all roster spots must remain filled except after supplemental Draft Waivers, and these empty spots must be filled immediately during the Supplemental Draft. Trades with other teams must involve identical roster positions to maintain a full roster. Multiple player trades may be made in order to adhere to this rule. Each team roster consists of 16 players in the following positions:

2 Quarterbacks
4 Running Backs (Half Backs & Full Backs)
6 Wide Receivers (Wide Receivers & Tight Ends)
2 Kickers
2 Defensive Teams

These exact numbers must be maintained and can never be exceeded. You can not stock extra players at one position at the expense of another position. Running backs can be any mix of Half and Full Backs, Wide Receivers can be any mix of WRs and Tight Ends. A player can not be selected to fill a roster position if he is not listed in that possition on the Official NFL team roster. Example: If Joe Smith, who plays for Seattle, is listed as a RB on Seattle's Official roster, then he can not occupy one of your WR slots even if he frequently lines up as a WR on the field. If a player is listed at multiple positions on the Official NFL roster, then he must fill the highest value position of those he is listed as. Value order is as follows (1 is highest): 1 - Kicker, 2 - Quarter Back, 3 - Running Back, 4 - Wide Receiver, 5 - Defensive Position. Example: If Joe Smith is listed on the Official NFL roster as a QB/WR, then he must occupy a QB slot on your roster, even if he spends most of his time in the WR position.