Ineligible receiver downfield
In gridiron football, ineligible receiver downfield is a penalty that is called when a forward pass is thrown and an ineligible receiver is beyond the line of scrimmage without blocking an opponent at the time of the pass. A member of the offensive team considered an eligible receiver by the rules of the game,in most leagues, are the running backs, wide receivers, and tight ends. Ineligible receivers include the center, offensive guards, and offensive tackles.
Further, any covered receiver on the line of scrimmage is ineligible. Numbers from 50-79 may not go pass either in 11 man football.